Sync with the latest Gnulib code (1a268176f)

1 files changed, 694 insertions, 121 deletions

diff --git a/gl/m4/gnulib-common.m4 b/gl/m4/gnulib-common.m4
index 0ae5a9ec..12b19dbc 100644
--- a/gl/m4/gnulib-common.m4
+++ b/gl/m4/gnulib-common.m4
@@ -1,25 +1,54 @@
-# gnulib-common.m4 serial 33
-dnl Copyright (C) 2007-2013 Free Software Foundation, Inc.
+# gnulib-common.m4 serial 67
+dnl Copyright (C) 2007-2021 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
 dnl with or without modifications, as long as this notice is preserved.
 
+AC_PREREQ([2.62])
+
 # gl_COMMON
 # is expanded unconditionally through gnulib-tool magic.
 AC_DEFUN([gl_COMMON], [
   dnl Use AC_REQUIRE here, so that the code is expanded once only.
   AC_REQUIRE([gl_00GNULIB])
   AC_REQUIRE([gl_COMMON_BODY])
+  AC_REQUIRE([gl_ZZGNULIB])
 ])
 AC_DEFUN([gl_COMMON_BODY], [
+  AH_VERBATIM([_GL_GNUC_PREREQ],
+[/* True if the compiler says it groks GNU C version MAJOR.MINOR.  */
+#if defined __GNUC__ && defined __GNUC_MINOR__
+# define _GL_GNUC_PREREQ(major, minor) \
+    ((major) < __GNUC__ + ((minor) <= __GNUC_MINOR__))
+#else
+# define _GL_GNUC_PREREQ(major, minor) 0
+#endif
+])
   AH_VERBATIM([_Noreturn],
 [/* The _Noreturn keyword of C11.  */
-#if ! (defined _Noreturn \
-       || (defined __STDC_VERSION__ && 201112 <= __STDC_VERSION__))
-# if (3 <= __GNUC__ || (__GNUC__ == 2 && 8 <= __GNUC_MINOR__) \
-      || 0x5110 <= __SUNPRO_C)
+#ifndef _Noreturn
+# if (defined __cplusplus \
+      && ((201103 <= __cplusplus && !(__GNUC__ == 4 && __GNUC_MINOR__ == 7)) \
+          || (defined _MSC_VER && 1900 <= _MSC_VER)) \
+      && 0)
+    /* [[noreturn]] is not practically usable, because with it the syntax
+         extern _Noreturn void func (...);
+       would not be valid; such a declaration would only be valid with 'extern'
+       and '_Noreturn' swapped, or without the 'extern' keyword.  However, some
+       AIX system header files and several gnulib header files use precisely
+       this syntax with 'extern'.  */
+#  define _Noreturn [[noreturn]]
+# elif ((!defined __cplusplus || defined __clang__) \
+        && (201112 <= (defined __STDC_VERSION__ ? __STDC_VERSION__ : 0) \
+            || (!defined __STRICT_ANSI__ \
+                && (_GL_GNUC_PREREQ (4, 7) \
+                    || (defined __apple_build_version__ \
+                        ? 6000000 <= __apple_build_version__ \
+                        : 3 < __clang_major__ + (5 <= __clang_minor__))))))
+   /* _Noreturn works as-is.  */
+# elif _GL_GNUC_PREREQ (2, 8) || defined __clang__ || 0x5110 <= __SUNPRO_C
 #  define _Noreturn __attribute__ ((__noreturn__))
-# elif defined _MSC_VER && 1200 <= _MSC_VER
+# elif 1200 <= (defined _MSC_VER ? _MSC_VER : 0)
 #  define _Noreturn __declspec (noreturn)
 # else
 #  define _Noreturn
@@ -36,33 +65,437 @@ AC_DEFUN([gl_COMMON_BODY], [
 #if defined __APPLE__ && defined __MACH__ && __APPLE_CC__ >= 5465 && !defined __cplusplus && __STDC_VERSION__ >= 199901L && !defined __GNUC_STDC_INLINE__
 # define __GNUC_STDC_INLINE__ 1
 #endif])
-  AH_VERBATIM([unused_parameter],
-[/* Define as a marker that can be attached to declarations that might not
-    be used.  This helps to reduce warnings, such as from
-    GCC -Wunused-parameter.  */
-#if __GNUC__ >= 3 || (__GNUC__ == 2 && __GNUC_MINOR__ >= 7)
-# define _GL_UNUSED __attribute__ ((__unused__))
+  AH_VERBATIM([attribute],
+[/* Attributes.  */
+#if (defined __has_attribute \
+     && (!defined __clang_minor__ \
+         || 3 < __clang_major__ + (5 <= __clang_minor__)))
+# define _GL_HAS_ATTRIBUTE(attr) __has_attribute (__##attr##__)
 #else
-# define _GL_UNUSED
+# define _GL_HAS_ATTRIBUTE(attr) _GL_ATTR_##attr
+# define _GL_ATTR_alloc_size _GL_GNUC_PREREQ (4, 3)
+# define _GL_ATTR_always_inline _GL_GNUC_PREREQ (3, 2)
+# define _GL_ATTR_artificial _GL_GNUC_PREREQ (4, 3)
+# define _GL_ATTR_cold _GL_GNUC_PREREQ (4, 3)
+# define _GL_ATTR_const _GL_GNUC_PREREQ (2, 95)
+# define _GL_ATTR_deprecated _GL_GNUC_PREREQ (3, 1)
+# define _GL_ATTR_diagnose_if 0
+# define _GL_ATTR_error _GL_GNUC_PREREQ (4, 3)
+# define _GL_ATTR_externally_visible _GL_GNUC_PREREQ (4, 1)
+# define _GL_ATTR_fallthrough _GL_GNUC_PREREQ (7, 0)
+# define _GL_ATTR_format _GL_GNUC_PREREQ (2, 7)
+# define _GL_ATTR_leaf _GL_GNUC_PREREQ (4, 6)
+# define _GL_ATTR_malloc _GL_GNUC_PREREQ (3, 0)
+# ifdef _ICC
+#  define _GL_ATTR_may_alias 0
+# else
+#  define _GL_ATTR_may_alias _GL_GNUC_PREREQ (3, 3)
+# endif
+# define _GL_ATTR_noinline _GL_GNUC_PREREQ (3, 1)
+# define _GL_ATTR_nonnull _GL_GNUC_PREREQ (3, 3)
+# define _GL_ATTR_nonstring _GL_GNUC_PREREQ (8, 0)
+# define _GL_ATTR_nothrow _GL_GNUC_PREREQ (3, 3)
+# define _GL_ATTR_packed _GL_GNUC_PREREQ (2, 7)
+# define _GL_ATTR_pure _GL_GNUC_PREREQ (2, 96)
+# define _GL_ATTR_returns_nonnull _GL_GNUC_PREREQ (4, 9)
+# define _GL_ATTR_sentinel _GL_GNUC_PREREQ (4, 0)
+# define _GL_ATTR_unused _GL_GNUC_PREREQ (2, 7)
+# define _GL_ATTR_warn_unused_result _GL_GNUC_PREREQ (3, 4)
 #endif
-/* The name _UNUSED_PARAMETER_ is an earlier spelling, although the name
-   is a misnomer outside of parameter lists.  */
-#define _UNUSED_PARAMETER_ _GL_UNUSED
 
-/* The __pure__ attribute was added in gcc 2.96.  */
-#if __GNUC__ > 2 || (__GNUC__ == 2 && __GNUC_MINOR__ >= 96)
-# define _GL_ATTRIBUTE_PURE __attribute__ ((__pure__))
+#ifdef __has_c_attribute
+# define _GL_HAS_C_ATTRIBUTE(attr) __has_c_attribute (__##attr##__)
+#else
+# define _GL_HAS_C_ATTRIBUTE(attr) 0
+#endif
+
+]dnl There is no _GL_ATTRIBUTE_ALIGNED; use stdalign's _Alignas instead.
+[
+/* _GL_ATTRIBUTE_ALLOC_SIZE ((N)) declares that the Nth argument of the function
+   is the size of the returned memory block.
+   _GL_ATTRIBUTE_ALLOC_SIZE ((M, N)) declares that the Mth argument multiplied
+   by the Nth argument of the function is the size of the returned memory block.
+ */
+/* Applies to: function, pointer to function, function types.  */
+#if _GL_HAS_ATTRIBUTE (alloc_size)
+# define _GL_ATTRIBUTE_ALLOC_SIZE(args) __attribute__ ((__alloc_size__ args))
+#else
+# define _GL_ATTRIBUTE_ALLOC_SIZE(args)
+#endif
+
+/* _GL_ATTRIBUTE_ALWAYS_INLINE tells that the compiler should always inline the
+   function and report an error if it cannot do so.  */
+/* Applies to: function.  */
+#if _GL_HAS_ATTRIBUTE (always_inline)
+# define _GL_ATTRIBUTE_ALWAYS_INLINE __attribute__ ((__always_inline__))
+#else
+# define _GL_ATTRIBUTE_ALWAYS_INLINE
+#endif
+
+/* _GL_ATTRIBUTE_ARTIFICIAL declares that the function is not important to show
+    in stack traces when debugging.  The compiler should omit the function from
+    stack traces.  */
+/* Applies to: function.  */
+#if _GL_HAS_ATTRIBUTE (artificial)
+# define _GL_ATTRIBUTE_ARTIFICIAL __attribute__ ((__artificial__))
+#else
+# define _GL_ATTRIBUTE_ARTIFICIAL
+#endif
+
+/* _GL_ATTRIBUTE_COLD declares that the function is rarely executed.  */
+/* Applies to: functions.  */
+/* Avoid __attribute__ ((cold)) on MinGW; see thread starting at
+   <https://lists.gnu.org/r/emacs-devel/2019-04/msg01152.html>.
+   Also, Oracle Studio 12.6 requires 'cold' not '__cold__'.  */
+#if _GL_HAS_ATTRIBUTE (cold) && !defined __MINGW32__
+# ifndef __SUNPRO_C
+#  define _GL_ATTRIBUTE_COLD __attribute__ ((__cold__))
+# else
+#  define _GL_ATTRIBUTE_COLD __attribute__ ((cold))
+# endif
 #else
-# define _GL_ATTRIBUTE_PURE /* empty */
+# define _GL_ATTRIBUTE_COLD
 #endif
 
-/* The __const__ attribute was added in gcc 2.95.  */
-#if __GNUC__ > 2 || (__GNUC__ == 2 && __GNUC_MINOR__ >= 95)
+/* _GL_ATTRIBUTE_CONST declares that it is OK for a compiler to omit duplicate
+   calls to the function with the same arguments.
+   This attribute is safe for a function that neither depends on nor affects
+   observable state, and always returns exactly once - e.g., does not loop
+   forever, and does not call longjmp.
+   (This attribute is stricter than _GL_ATTRIBUTE_PURE.)  */
+/* Applies to: functions.  */
+#if _GL_HAS_ATTRIBUTE (const)
 # define _GL_ATTRIBUTE_CONST __attribute__ ((__const__))
 #else
-# define _GL_ATTRIBUTE_CONST /* empty */
+# define _GL_ATTRIBUTE_CONST
+#endif
+
+/* _GL_ATTRIBUTE_DEALLOC (F, I) declares that the function returns pointers
+   that can be freed by passing them as the Ith argument to the
+   function F.
+   _GL_ATTRIBUTE_DEALLOC_FREE declares that the function returns pointers that
+   can be freed via 'free'; it can be used only after declaring 'free'.  */
+/* Applies to: functions.  Cannot be used on inline functions.  */
+#if _GL_GNUC_PREREQ (11, 0)
+# define _GL_ATTRIBUTE_DEALLOC(f, i) __attribute__ ((__malloc__ (f, i)))
+#else
+# define _GL_ATTRIBUTE_DEALLOC(f, i)
+#endif
+#define _GL_ATTRIBUTE_DEALLOC_FREE _GL_ATTRIBUTE_DEALLOC (free, 1)
+
+/* _GL_ATTRIBUTE_DEPRECATED: Declares that an entity is deprecated.
+   The compiler may warn if the entity is used.  */
+/* Applies to:
+     - function, variable,
+     - struct, union, struct/union member,
+     - enumeration, enumeration item,
+     - typedef,
+   in C++ also: namespace, class, template specialization.  */
+#if _GL_HAS_C_ATTRIBUTE (deprecated)
+# define _GL_ATTRIBUTE_DEPRECATED [[__deprecated__]]
+#elif _GL_HAS_ATTRIBUTE (deprecated)
+# define _GL_ATTRIBUTE_DEPRECATED __attribute__ ((__deprecated__))
+#else
+# define _GL_ATTRIBUTE_DEPRECATED
+#endif
+
+/* _GL_ATTRIBUTE_ERROR(msg) requests an error if a function is called and
+   the function call is not optimized away.
+   _GL_ATTRIBUTE_WARNING(msg) requests a warning if a function is called and
+   the function call is not optimized away.  */
+/* Applies to: functions.  */
+#if _GL_HAS_ATTRIBUTE (error)
+# define _GL_ATTRIBUTE_ERROR(msg) __attribute__ ((__error__ (msg)))
+# define _GL_ATTRIBUTE_WARNING(msg) __attribute__ ((__warning__ (msg)))
+#elif _GL_HAS_ATTRIBUTE (diagnose_if)
+# define _GL_ATTRIBUTE_ERROR(msg) __attribute__ ((__diagnose_if__ (1, msg, "error")))
+# define _GL_ATTRIBUTE_WARNING(msg) __attribute__ ((__diagnose_if__ (1, msg, "warning")))
+#else
+# define _GL_ATTRIBUTE_ERROR(msg)
+# define _GL_ATTRIBUTE_WARNING(msg)
+#endif
+
+/* _GL_ATTRIBUTE_EXTERNALLY_VISIBLE declares that the entity should remain
+   visible to debuggers etc., even with '-fwhole-program'.  */
+/* Applies to: functions, variables.  */
+#if _GL_HAS_ATTRIBUTE (externally_visible)
+# define _GL_ATTRIBUTE_EXTERNALLY_VISIBLE __attribute__ ((externally_visible))
+#else
+# define _GL_ATTRIBUTE_EXTERNALLY_VISIBLE
+#endif
+
+/* _GL_ATTRIBUTE_FALLTHROUGH declares that it is not a programming mistake if
+   the control flow falls through to the immediately following 'case' or
+   'default' label.  The compiler should not warn in this case.  */
+/* Applies to: Empty statement (;), inside a 'switch' statement.  */
+/* Always expands to something.  */
+#if _GL_HAS_C_ATTRIBUTE (fallthrough)
+# define _GL_ATTRIBUTE_FALLTHROUGH [[__fallthrough__]]
+#elif _GL_HAS_ATTRIBUTE (fallthrough)
+# define _GL_ATTRIBUTE_FALLTHROUGH __attribute__ ((__fallthrough__))
+#else
+# define _GL_ATTRIBUTE_FALLTHROUGH ((void) 0)
+#endif
+
+/* _GL_ATTRIBUTE_FORMAT ((ARCHETYPE, STRING-INDEX, FIRST-TO-CHECK))
+   declares that the STRING-INDEXth function argument is a format string of
+   style ARCHETYPE, which is one of:
+     printf, gnu_printf
+     scanf, gnu_scanf,
+     strftime, gnu_strftime,
+     strfmon,
+   or the same thing prefixed and suffixed with '__'.
+   If FIRST-TO-CHECK is not 0, arguments starting at FIRST-TO_CHECK
+   are suitable for the format string.  */
+/* Applies to: functions.  */
+#if _GL_HAS_ATTRIBUTE (format)
+# define _GL_ATTRIBUTE_FORMAT(spec) __attribute__ ((__format__ spec))
+#else
+# define _GL_ATTRIBUTE_FORMAT(spec)
+#endif
+
+/* _GL_ATTRIBUTE_LEAF declares that if the function is called from some other
+   compilation unit, it executes code from that unit only by return or by
+   exception handling.  This declaration lets the compiler optimize that unit
+   more aggressively.  */
+/* Applies to: functions.  */
+#if _GL_HAS_ATTRIBUTE (leaf)
+# define _GL_ATTRIBUTE_LEAF __attribute__ ((__leaf__))
+#else
+# define _GL_ATTRIBUTE_LEAF
+#endif
+
+/* _GL_ATTRIBUTE_MALLOC declares that the function returns a pointer to freshly
+   allocated memory.  */
+/* Applies to: functions.  */
+#if _GL_HAS_ATTRIBUTE (malloc)
+# define _GL_ATTRIBUTE_MALLOC __attribute__ ((__malloc__))
+#else
+# define _GL_ATTRIBUTE_MALLOC
+#endif
+
+/* _GL_ATTRIBUTE_MAY_ALIAS declares that pointers to the type may point to the
+   same storage as pointers to other types.  Thus this declaration disables
+   strict aliasing optimization.  */
+/* Applies to: types.  */
+/* Oracle Studio 12.6 mishandles may_alias despite __has_attribute OK.  */
+#if _GL_HAS_ATTRIBUTE (may_alias) && !defined __SUNPRO_C
+# define _GL_ATTRIBUTE_MAY_ALIAS __attribute__ ((__may_alias__))
+#else
+# define _GL_ATTRIBUTE_MAY_ALIAS
+#endif
+
+/* _GL_ATTRIBUTE_MAYBE_UNUSED declares that it is not a programming mistake if
+   the entity is not used.  The compiler should not warn if the entity is not
+   used.  */
+/* Applies to:
+     - function, variable,
+     - struct, union, struct/union member,
+     - enumeration, enumeration item,
+     - typedef,
+   in C++ also: class.  */
+/* In C++ and C2x, this is spelled [[__maybe_unused__]].
+   GCC's syntax is __attribute__ ((__unused__)).
+   clang supports both syntaxes.  */
+#if _GL_HAS_C_ATTRIBUTE (maybe_unused)
+# define _GL_ATTRIBUTE_MAYBE_UNUSED [[__maybe_unused__]]
+#else
+# define _GL_ATTRIBUTE_MAYBE_UNUSED _GL_ATTRIBUTE_UNUSED
+#endif
+/* Alternative spelling of this macro, for convenience.  */
+#define _GL_UNUSED _GL_ATTRIBUTE_MAYBE_UNUSED
+/* Earlier spellings of this macro.  */
+#define _UNUSED_PARAMETER_ _GL_ATTRIBUTE_MAYBE_UNUSED
+
+/* _GL_ATTRIBUTE_NODISCARD declares that the caller of the function should not
+   discard the return value.  The compiler may warn if the caller does not use
+   the return value, unless the caller uses something like ignore_value.  */
+/* Applies to: function, enumeration, class.  */
+#if _GL_HAS_C_ATTRIBUTE (nodiscard)
+# define _GL_ATTRIBUTE_NODISCARD [[__nodiscard__]]
+#elif _GL_HAS_ATTRIBUTE (warn_unused_result)
+# define _GL_ATTRIBUTE_NODISCARD __attribute__ ((__warn_unused_result__))
+#else
+# define _GL_ATTRIBUTE_NODISCARD
+#endif
+
+/* _GL_ATTRIBUTE_NOINLINE tells that the compiler should not inline the
+   function.  */
+/* Applies to: functions.  */
+#if _GL_HAS_ATTRIBUTE (noinline)
+# define _GL_ATTRIBUTE_NOINLINE __attribute__ ((__noinline__))
+#else
+# define _GL_ATTRIBUTE_NOINLINE
+#endif
+
+/* _GL_ATTRIBUTE_NONNULL ((N1, N2,...)) declares that the arguments N1, N2,...
+   must not be NULL.
+   _GL_ATTRIBUTE_NONNULL () declares that all pointer arguments must not be
+   null.  */
+/* Applies to: functions.  */
+#if _GL_HAS_ATTRIBUTE (nonnull)
+# define _GL_ATTRIBUTE_NONNULL(args) __attribute__ ((__nonnull__ args))
+#else
+# define _GL_ATTRIBUTE_NONNULL(args)
+#endif
+
+/* _GL_ATTRIBUTE_NONSTRING declares that the contents of a character array is
+   not meant to be NUL-terminated.  */
+/* Applies to: struct/union members and variables that are arrays of element
+   type '[[un]signed] char'.  */
+#if _GL_HAS_ATTRIBUTE (nonstring)
+# define _GL_ATTRIBUTE_NONSTRING __attribute__ ((__nonstring__))
+#else
+# define _GL_ATTRIBUTE_NONSTRING
+#endif
+
+/* There is no _GL_ATTRIBUTE_NORETURN; use _Noreturn instead.  */
+
+/* _GL_ATTRIBUTE_NOTHROW declares that the function does not throw exceptions.
+ */
+/* Applies to: functions.  */
+#if _GL_HAS_ATTRIBUTE (nothrow) && !defined __cplusplus
+# define _GL_ATTRIBUTE_NOTHROW __attribute__ ((__nothrow__))
+#else
+# define _GL_ATTRIBUTE_NOTHROW
+#endif
+
+/* _GL_ATTRIBUTE_PACKED declares:
+   For struct members: The member has the smallest possible alignment.
+   For struct, union, class: All members have the smallest possible alignment,
+   minimizing the memory required.  */
+/* Applies to: struct members, struct, union,
+   in C++ also: class.  */
+#if _GL_HAS_ATTRIBUTE (packed)
+# define _GL_ATTRIBUTE_PACKED __attribute__ ((__packed__))
+#else
+# define _GL_ATTRIBUTE_PACKED
+#endif
+
+/* _GL_ATTRIBUTE_PURE declares that It is OK for a compiler to omit duplicate
+   calls to the function with the same arguments if observable state is not
+   changed between calls.
+   This attribute is safe for a function that does not affect
+   observable state, and always returns exactly once.
+   (This attribute is looser than _GL_ATTRIBUTE_CONST.)  */
+/* Applies to: functions.  */
+#if _GL_HAS_ATTRIBUTE (pure)
+# define _GL_ATTRIBUTE_PURE __attribute__ ((__pure__))
+#else
+# define _GL_ATTRIBUTE_PURE
+#endif
+
+/* _GL_ATTRIBUTE_RETURNS_NONNULL declares that the function's return value is
+   a non-NULL pointer.  */
+/* Applies to: functions.  */
+#if _GL_HAS_ATTRIBUTE (returns_nonnull)
+# define _GL_ATTRIBUTE_RETURNS_NONNULL __attribute__ ((__returns_nonnull__))
+#else
+# define _GL_ATTRIBUTE_RETURNS_NONNULL
+#endif
+
+/* _GL_ATTRIBUTE_SENTINEL(pos) declares that the variadic function expects a
+   trailing NULL argument.
+   _GL_ATTRIBUTE_SENTINEL () - The last argument is NULL (requires C99).
+   _GL_ATTRIBUTE_SENTINEL ((N)) - The (N+1)st argument from the end is NULL.  */
+/* Applies to: functions.  */
+#if _GL_HAS_ATTRIBUTE (sentinel)
+# define _GL_ATTRIBUTE_SENTINEL(pos) __attribute__ ((__sentinel__ pos))
+#else
+# define _GL_ATTRIBUTE_SENTINEL(pos)
+#endif
+
+/* A helper macro.  Don't use it directly.  */
+#if _GL_HAS_ATTRIBUTE (unused)
+# define _GL_ATTRIBUTE_UNUSED __attribute__ ((__unused__))
+#else
+# define _GL_ATTRIBUTE_UNUSED
+#endif
+
+]dnl There is no _GL_ATTRIBUTE_VISIBILITY; see m4/visibility.m4 instead.
+[
+/* _GL_UNUSED_LABEL; declares that it is not a programming mistake if the
+   immediately preceding label is not used.  The compiler should not warn
+   if the label is not used.  */
+/* Applies to: label (both in C and C++).  */
+/* Note that g++ < 4.5 does not support the '__attribute__ ((__unused__)) ;'
+   syntax.  But clang does.  */
+#if !(defined __cplusplus && !_GL_GNUC_PREREQ (4, 5)) || defined __clang__
+# define _GL_UNUSED_LABEL _GL_ATTRIBUTE_UNUSED
+#else
+# define _GL_UNUSED_LABEL
 #endif
 ])
+  AH_VERBATIM([async_safe],
+[/* The _GL_ASYNC_SAFE marker should be attached to functions that are
+   signal handlers (for signals other than SIGABRT, SIGPIPE) or can be
+   invoked from such signal handlers.  Such functions have some restrictions:
+     * All functions that it calls should be marked _GL_ASYNC_SAFE as well,
+       or should be listed as async-signal-safe in POSIX
+       <https://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html#tag_15_04>
+       section 2.4.3.  Note that malloc(), sprintf(), and fwrite(), in
+       particular, are NOT async-signal-safe.
+     * All memory locations (variables and struct fields) that these functions
+       access must be marked 'volatile'.  This holds for both read and write
+       accesses.  Otherwise the compiler might optimize away stores to and
+       reads from such locations that occur in the program, depending on its
+       data flow analysis.  For example, when the program contains a loop
+       that is intended to inspect a variable set from within a signal handler
+           while (!signal_occurred)
+             ;
+       the compiler is allowed to transform this into an endless loop if the
+       variable 'signal_occurred' is not declared 'volatile'.
+   Additionally, recall that:
+     * A signal handler should not modify errno (except if it is a handler
+       for a fatal signal and ends by raising the same signal again, thus
+       provoking the termination of the process).  If it invokes a function
+       that may clobber errno, it needs to save and restore the value of
+       errno.  */
+#define _GL_ASYNC_SAFE
+])
+  AH_VERBATIM([micro_optimizations],
+[/* _GL_CMP (n1, n2) performs a three-valued comparison on n1 vs. n2, where
+   n1 and n2 are expressions without side effects, that evaluate to real
+   numbers (excluding NaN).
+   It returns
+     1  if n1 > n2
+     0  if n1 == n2
+     -1 if n1 < n2
+   The naïve code   (n1 > n2 ? 1 : n1 < n2 ? -1 : 0)  produces a conditional
+   jump with nearly all GCC versions up to GCC 10.
+   This variant     (n1 < n2 ? -1 : n1 > n2)  produces a conditional with many
+   GCC versions up to GCC 9.
+   The better code  (n1 > n2) - (n1 < n2)  from Hacker's Delight § 2-9
+   avoids conditional jumps in all GCC versions >= 3.4.  */
+#define _GL_CMP(n1, n2) (((n1) > (n2)) - ((n1) < (n2)))
+])
+  dnl Hint which direction to take regarding cross-compilation guesses:
+  dnl When a user installs a program on a platform they are not intimately
+  dnl familiar with, --enable-cross-guesses=conservative is the appropriate
+  dnl choice.  It implements the "If we don't know, assume the worst" principle.
+  dnl However, when an operating system developer (on a platform which is not
+  dnl yet known to gnulib) builds packages for their platform, they want to
+  dnl expose, not hide, possible platform bugs; in this case,
+  dnl --enable-cross-guesses=risky is the appropriate choice.
+  dnl Sets the variables
+  dnl gl_cross_guess_normal    (to be used when 'yes' is good and 'no' is bad),
+  dnl gl_cross_guess_inverted  (to be used when 'no' is good and 'yes' is bad).
+  AC_ARG_ENABLE([cross-guesses],
+    [AS_HELP_STRING([--enable-cross-guesses={conservative|risky}],
+       [specify policy for cross-compilation guesses])],
+    [if test "x$enableval" != xconservative && test "x$enableval" != xrisky; then
+       AC_MSG_WARN([invalid argument supplied to --enable-cross-guesses])
+       enableval=conservative
+     fi
+     gl_cross_guesses="$enableval"],
+    [gl_cross_guesses=conservative])
+  if test $gl_cross_guesses = risky; then
+    gl_cross_guess_normal="guessing yes"
+    gl_cross_guess_inverted="guessing no"
+  else
+    gl_cross_guess_normal="guessing no"
+    gl_cross_guess_inverted="guessing yes"
+  fi
   dnl Preparation for running test programs:
   dnl Tell glibc to write diagnostics from -D_FORTIFY_SOURCE=2 to stderr, not
   dnl to /dev/tty, so they can be redirected to log files.  Such diagnostics
@@ -71,6 +504,16 @@ AC_DEFUN([gl_COMMON_BODY], [
   export LIBC_FATAL_STDERR_
 ])
 
+# gl_MODULE_INDICATOR_INIT_VARIABLE([variablename])
+# gl_MODULE_INDICATOR_INIT_VARIABLE([variablename], [initialvalue])
+# initializes the shell variable that indicates the presence of the given module
+# as a C preprocessor expression.
+AC_DEFUN([gl_MODULE_INDICATOR_INIT_VARIABLE],
+[
+  GL_MODULE_INDICATOR_PREFIX[]_[$1]=m4_if([$2], , [0], [$2])
+  AC_SUBST(GL_MODULE_INDICATOR_PREFIX[]_[$1])
+])
+
 # gl_MODULE_INDICATOR_CONDITION
 # expands to a C preprocessor expression that evaluates to 1 or 0, depending
 # whether a gnulib module that has been requested shall be considered present
@@ -83,9 +526,9 @@ m4_define([gl_MODULE_INDICATOR_CONDITION], [1])
 AC_DEFUN([gl_MODULE_INDICATOR_SET_VARIABLE],
 [
   gl_MODULE_INDICATOR_SET_VARIABLE_AUX(
-    [GNULIB_[]m4_translit([[$1]],
-                          [abcdefghijklmnopqrstuvwxyz./-],
-                          [ABCDEFGHIJKLMNOPQRSTUVWXYZ___])],
+    [GL_MODULE_INDICATOR_PREFIX[]_GNULIB_[]m4_translit([[$1]],
+                                                       [abcdefghijklmnopqrstuvwxyz./-],
+                                                       [ABCDEFGHIJKLMNOPQRSTUVWXYZ___])],
     [gl_MODULE_INDICATOR_CONDITION])
 ])
 
@@ -197,42 +640,20 @@ AC_DEFUN([gl_FEATURES_H],
   AC_SUBST([HAVE_FEATURES_H])
 ])
 
-# m4_foreach_w
-# is a backport of autoconf-2.59c's m4_foreach_w.
-# Remove this macro when we can assume autoconf >= 2.60.
-m4_ifndef([m4_foreach_w],
-  [m4_define([m4_foreach_w],
-    [m4_foreach([$1], m4_split(m4_normalize([$2]), [ ]), [$3])])])
-
-# AS_VAR_IF(VAR, VALUE, [IF-MATCH], [IF-NOT-MATCH])
-# ----------------------------------------------------
-# Backport of autoconf-2.63b's macro.
-# Remove this macro when we can assume autoconf >= 2.64.
-m4_ifndef([AS_VAR_IF],
-[m4_define([AS_VAR_IF],
-[AS_IF([test x"AS_VAR_GET([$1])" = x""$2], [$3], [$4])])])
-
 # gl_PROG_CC_C99
 # Modifies the value of the shell variable CC in an attempt to make $CC
 # understand ISO C99 source code.
-# This is like AC_PROG_CC_C99, except that
-# - AC_PROG_CC_C99 did not exist in Autoconf versions < 2.60,
-# - AC_PROG_CC_C99 does not mix well with AC_PROG_CC_STDC
-#   <http://lists.gnu.org/archive/html/bug-gnulib/2011-09/msg00367.html>,
-#   but many more packages use AC_PROG_CC_STDC than AC_PROG_CC_C99
-#   <http://lists.gnu.org/archive/html/bug-gnulib/2011-09/msg00441.html>.
-# Remaining problems:
-# - When AC_PROG_CC_STDC is invoked twice, it adds the C99 enabling options
-#   to CC twice
-#   <http://lists.gnu.org/archive/html/bug-gnulib/2011-09/msg00431.html>.
-# - AC_PROG_CC_STDC is likely to change now that C11 is an ISO standard.
 AC_DEFUN([gl_PROG_CC_C99],
 [
-  dnl Change that version number to the minimum Autoconf version that supports
-  dnl mixing AC_PROG_CC_C99 calls with AC_PROG_CC_STDC calls.
-  m4_version_prereq([9.0],
-    [AC_REQUIRE([AC_PROG_CC_C99])],
-    [AC_REQUIRE([AC_PROG_CC_STDC])])
+  dnl Just use AC_PROG_CC_C99.
+  dnl When AC_PROG_CC_C99 and AC_PROG_CC_STDC are used together, the substituted
+  dnl value of CC will contain the C99 enabling options twice. But this is only
+  dnl a cosmetic problem.
+  dnl With Autoconf >= 2.70, use AC_PROG_CC since it implies AC_PROG_CC_C99;
+  dnl this avoids a "warning: The macro `AC_PROG_CC_C99' is obsolete."
+  m4_version_prereq([2.70],
+    [AC_REQUIRE([AC_PROG_CC])],
+    [AC_REQUIRE([AC_PROG_CC_C99])])
 ])
 
 # gl_PROG_AR_RANLIB
@@ -243,9 +664,11 @@ AC_DEFUN([gl_PROG_AR_RANLIB],
 [
   dnl Minix 3 comes with two toolchains: The Amsterdam Compiler Kit compiler
   dnl as "cc", and GCC as "gcc". They have different object file formats and
-  dnl library formats. In particular, the GNU binutils programs ar, ranlib
+  dnl library formats. In particular, the GNU binutils programs ar and ranlib
   dnl produce libraries that work only with gcc, not with cc.
   AC_REQUIRE([AC_PROG_CC])
+  dnl The '][' hides this use from 'aclocal'.
+  AC_BEFORE([$0], [A][M_PROG_AR])
   AC_CACHE_CHECK([for Minix Amsterdam compiler], [gl_cv_c_amsterdam_compiler],
     [
       AC_EGREP_CPP([Amsterdam],
@@ -257,25 +680,39 @@ Amsterdam
         [gl_cv_c_amsterdam_compiler=yes],
         [gl_cv_c_amsterdam_compiler=no])
     ])
-  if test -z "$AR"; then
-    if test $gl_cv_c_amsterdam_compiler = yes; then
+
+  dnl Don't compete with AM_PROG_AR's decision about AR/ARFLAGS if we are not
+  dnl building with __ACK__.
+  if test $gl_cv_c_amsterdam_compiler = yes; then
+    if test -z "$AR"; then
       AR='cc -c.a'
-      if test -z "$ARFLAGS"; then
-        ARFLAGS='-o'
-      fi
-    else
-      dnl Use the Automake-documented default values for AR and ARFLAGS,
-      dnl but prefer ${host}-ar over ar (useful for cross-compiling).
-      AC_CHECK_TOOL([AR], [ar], [ar])
-      if test -z "$ARFLAGS"; then
-        ARFLAGS='cru'
-      fi
     fi
-  else
     if test -z "$ARFLAGS"; then
-      ARFLAGS='cru'
+      ARFLAGS='-o'
     fi
+  else
+    dnl AM_PROG_AR was added in automake v1.11.2.  AM_PROG_AR does not AC_SUBST
+    dnl ARFLAGS variable (it is filed into Makefile.in directly by automake
+    dnl script on-demand, if not specified by ./configure of course).
+    dnl Don't AC_REQUIRE the AM_PROG_AR otherwise the code for __ACK__ above
+    dnl will be ignored.  Also, pay attention to call AM_PROG_AR in else block
+    dnl because AM_PROG_AR is written so it could re-set AR variable even for
+    dnl __ACK__.  It may seem like its easier to avoid calling the macro here,
+    dnl but we need to AC_SUBST both AR/ARFLAGS (thus those must have some good
+    dnl default value and automake should usually know them).
+    dnl
+    dnl The '][' hides this use from 'aclocal'.
+    m4_ifdef([A][M_PROG_AR], [A][M_PROG_AR], [:])
+  fi
+
+  dnl In case the code above has not helped with setting AR/ARFLAGS, use
+  dnl Automake-documented default values for AR and ARFLAGS, but prefer
+  dnl ${host}-ar over ar (useful for cross-compiling).
+  AC_CHECK_TOOL([AR], [ar], [ar])
+  if test -z "$ARFLAGS"; then
+    ARFLAGS='cr'
   fi
+
   AC_SUBST([AR])
   AC_SUBST([ARFLAGS])
   if test -z "$RANLIB"; then
@@ -289,46 +726,29 @@ Amsterdam
   AC_SUBST([RANLIB])
 ])
 
-# AC_PROG_MKDIR_P
-# is a backport of autoconf-2.60's AC_PROG_MKDIR_P, with a fix
-# for interoperability with automake-1.9.6 from autoconf-2.62.
-# Remove this macro when we can assume autoconf >= 2.62 or
-# autoconf >= 2.60 && automake >= 1.10.
-# AC_AUTOCONF_VERSION was introduced in 2.62, so use that as the witness.
-m4_ifndef([AC_AUTOCONF_VERSION],[
-m4_ifdef([AC_PROG_MKDIR_P], [
-  dnl For automake-1.9.6 && autoconf < 2.62: Ensure MKDIR_P is AC_SUBSTed.
-  m4_define([AC_PROG_MKDIR_P],
-    m4_defn([AC_PROG_MKDIR_P])[
-    AC_SUBST([MKDIR_P])])], [
-  dnl For autoconf < 2.60: Backport of AC_PROG_MKDIR_P.
-  AC_DEFUN_ONCE([AC_PROG_MKDIR_P],
-    [AC_REQUIRE([AM_PROG_MKDIR_P])dnl defined by automake
-     MKDIR_P='$(mkdir_p)'
-     AC_SUBST([MKDIR_P])])])
-])
-
 # AC_C_RESTRICT
-# This definition overrides the AC_C_RESTRICT macro from autoconf 2.60..2.61,
-# so that mixed use of GNU C and GNU C++ and mixed use of Sun C and Sun C++
-# works.
-# This definition can be removed once autoconf >= 2.62 can be assumed.
-# AC_AUTOCONF_VERSION was introduced in 2.62, so use that as the witness.
-m4_ifndef([AC_AUTOCONF_VERSION],[
+# This definition is copied from post-2.70 Autoconf and overrides the
+# AC_C_RESTRICT macro from autoconf 2.60..2.70.
+m4_version_prereq([2.70.1], [], [
 AC_DEFUN([AC_C_RESTRICT],
 [AC_CACHE_CHECK([for C/C++ restrict keyword], [ac_cv_c_restrict],
   [ac_cv_c_restrict=no
-   # The order here caters to the fact that C++ does not require restrict.
-   for ac_kw in __restrict __restrict__ _Restrict restrict; do
-     AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
-      [[typedef int * int_ptr;
-        int foo (int_ptr $ac_kw ip) {
-        return ip[0];
-       }]],
-      [[int s[1];
-        int * $ac_kw t = s;
-        t[0] = 0;
-        return foo(t)]])],
+   # Put '__restrict__' first, to avoid problems with glibc and non-GCC; see:
+   # https://lists.gnu.org/archive/html/bug-autoconf/2016-02/msg00006.html
+   # Put 'restrict' last, because C++ lacks it.
+   for ac_kw in __restrict__ __restrict _Restrict restrict; do
+     AC_COMPILE_IFELSE(
+      [AC_LANG_PROGRAM(
+         [[typedef int *int_ptr;
+           int foo (int_ptr $ac_kw ip) { return ip[0]; }
+           int bar (int [$ac_kw]); /* Catch GCC bug 14050.  */
+           int bar (int ip[$ac_kw]) { return ip[0]; }
+         ]],
+         [[int s[1];
+           int *$ac_kw t = s;
+           t[0] = 0;
+           return foo (t) + bar (t);
+         ]])],
       [ac_cv_c_restrict=$ac_kw])
      test "$ac_cv_c_restrict" != no && break
    done
@@ -336,22 +756,24 @@ AC_DEFUN([AC_C_RESTRICT],
  AH_VERBATIM([restrict],
 [/* Define to the equivalent of the C99 'restrict' keyword, or to
    nothing if this is not supported.  Do not define if restrict is
-   supported directly.  */
+   supported only directly.  */
 #undef restrict
-/* Work around a bug in Sun C++: it does not support _Restrict, even
-   though the corresponding Sun C compiler does, which causes
-   "#define restrict _Restrict" in the previous line.  Perhaps some future
-   version of Sun C++ will work with _Restrict; if so, it'll probably
-   define __RESTRICT, just as Sun C does.  */
-#if defined __SUNPRO_CC && !defined __RESTRICT
+/* Work around a bug in older versions of Sun C++, which did not
+   #define __restrict__ or support _Restrict or __restrict__
+   even though the corresponding Sun C compiler ended up with
+   "#define restrict _Restrict" or "#define restrict __restrict__"
+   in the previous line.  This workaround can be removed once
+   we assume Oracle Developer Studio 12.5 (2016) or later.  */
+#if defined __SUNPRO_CC && !defined __RESTRICT && !defined __restrict__
 # define _Restrict
+# define __restrict__
 #endif])
  case $ac_cv_c_restrict in
    restrict) ;;
    no) AC_DEFINE([restrict], []) ;;
    *)  AC_DEFINE_UNQUOTED([restrict], [$ac_cv_c_restrict]) ;;
  esac
-])
+])# AC_C_RESTRICT
 ])
 
 # gl_BIGENDIAN
@@ -363,6 +785,22 @@ AC_DEFUN([gl_BIGENDIAN],
   AC_C_BIGENDIAN
 ])
 
+# A temporary file descriptor.
+# Must be less than 10, because dash 0.5.8 does not support redirections
+# with multi-digit file descriptors.
+m4_define([GL_TMP_FD], 9)
+
+# gl_SILENT(command)
+# executes command, but without the normal configure output.
+# This is useful when you want to invoke AC_CACHE_CHECK (or AC_CHECK_FUNC etc.)
+# inside another AC_CACHE_CHECK.
+AC_DEFUN([gl_SILENT],
+[
+  exec GL_TMP_FD>&AS_MESSAGE_FD AS_MESSAGE_FD>/dev/null
+  $1
+  exec AS_MESSAGE_FD>&GL_TMP_FD GL_TMP_FD>&-
+])
+
 # gl_CACHE_VAL_SILENT(cache-id, command-to-set-it)
 # is like AC_CACHE_VAL(cache-id, command-to-set-it), except that it does not
 # output a spurious "(cached)" mark in the midst of other configure output.
@@ -370,8 +808,143 @@ AC_DEFUN([gl_BIGENDIAN],
 # by an AC_MSG_CHECKING/AC_MSG_RESULT pair.
 AC_DEFUN([gl_CACHE_VAL_SILENT],
 [
-  saved_as_echo_n="$as_echo_n"
-  as_echo_n=':'
-  AC_CACHE_VAL([$1], [$2])
-  as_echo_n="$saved_as_echo_n"
+  gl_SILENT([
+    AC_CACHE_VAL([$1], [$2])
+  ])
+])
+
+# gl_CC_ALLOW_WARNINGS
+# sets and substitutes a variable GL_CFLAG_ALLOW_WARNINGS, to a $(CC) option
+# that reverts a preceding '-Werror' option, if available.
+# This is expected to be '-Wno-error' on gcc, clang (except clang/MSVC), xlclang
+# and empty otherwise.
+AC_DEFUN([gl_CC_ALLOW_WARNINGS],
+[
+  AC_REQUIRE([AC_PROG_CC])
+  AC_CACHE_CHECK([for C compiler option to allow warnings],
+    [gl_cv_cc_wallow],
+    [rm -f conftest*
+     echo 'int dummy;' > conftest.c
+     AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS -c conftest.c 2>conftest1.err]) >/dev/null
+     AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS -Wno-error -c conftest.c 2>conftest2.err]) >/dev/null
+     dnl Test the number of error output lines, because AIX xlc accepts the
+     dnl option '-Wno-error', just to produce a warning
+     dnl "Option -Wno-error was incorrectly specified. The option will be ignored."
+     dnl afterwards.
+     if test $? = 0 && test `wc -l < conftest1.err` = `wc -l < conftest2.err`; then
+       gl_cv_cc_wallow='-Wno-error'
+     else
+       gl_cv_cc_wallow=none
+     fi
+     rm -f conftest*
+    ])
+  case "$gl_cv_cc_wallow" in
+    none) GL_CFLAG_ALLOW_WARNINGS='' ;;
+    *)    GL_CFLAG_ALLOW_WARNINGS="$gl_cv_cc_wallow" ;;
+  esac
+  AC_SUBST([GL_CFLAG_ALLOW_WARNINGS])
+])
+
+# gl_CXX_ALLOW_WARNINGS
+# sets and substitutes a variable GL_CXXFLAG_ALLOW_WARNINGS, to a $(CC) option
+# that reverts a preceding '-Werror' option, if available.
+AC_DEFUN([gl_CXX_ALLOW_WARNINGS],
+[
+  dnl Requires AC_PROG_CXX or gl_PROG_ANSI_CXX.
+  if test -n "$CXX" && test "$CXX" != no; then
+    AC_CACHE_CHECK([for C++ compiler option to allow warnings],
+      [gl_cv_cxx_wallow],
+      [rm -f conftest*
+       echo 'int dummy;' > conftest.cc
+       AC_TRY_COMMAND([${CXX-c++} $CXXFLAGS $CPPFLAGS -c conftest.cc 2>conftest1.err]) >/dev/null
+       AC_TRY_COMMAND([${CXX-c++} $CXXFLAGS $CPPFLAGS -Wno-error -c conftest.cc 2>conftest2.err]) >/dev/null
+       dnl Test the number of error output lines, because AIX xlC accepts the
+       dnl option '-Wno-error', just to produce a warning
+       dnl "Option -Wno-error was incorrectly specified. The option will be ignored."
+       dnl afterwards.
+       if test $? = 0 && test `wc -l < conftest1.err` = `wc -l < conftest2.err`; then
+         gl_cv_cxx_wallow='-Wno-error'
+       else
+         gl_cv_cxx_wallow=none
+       fi
+       rm -f conftest*
+      ])
+    case "$gl_cv_cxx_wallow" in
+      none) GL_CXXFLAG_ALLOW_WARNINGS='' ;;
+      *)    GL_CXXFLAG_ALLOW_WARNINGS="$gl_cv_cxx_wallow" ;;
+    esac
+  else
+    GL_CXXFLAG_ALLOW_WARNINGS=''
+  fi
+  AC_SUBST([GL_CXXFLAG_ALLOW_WARNINGS])
+])
+
+dnl Expands to some code for use in .c programs that, on native Windows, defines
+dnl the Microsoft deprecated alias function names to the underscore-prefixed
+dnl actual function names. With this macro, these function names are available
+dnl without linking with '-loldnames' and without generating warnings.
+dnl Usage: Use it after all system header files are included.
+dnl          #include <...>
+dnl          #include <...>
+dnl          ]GL_MDA_DEFINES[
+dnl          ...
+AC_DEFUN([GL_MDA_DEFINES],[
+AC_REQUIRE([_GL_MDA_DEFINES])
+[$gl_mda_defines]
+])
+AC_DEFUN([_GL_MDA_DEFINES],
+[gl_mda_defines='
+#if defined _WIN32 && !defined __CYGWIN__
+#define access    _access
+#define chdir     _chdir
+#define chmod     _chmod
+#define close     _close
+#define creat     _creat
+#define dup       _dup
+#define dup2      _dup2
+#define ecvt      _ecvt
+#define execl     _execl
+#define execle    _execle
+#define execlp    _execlp
+#define execv     _execv
+#define execve    _execve
+#define execvp    _execvp
+#define execvpe   _execvpe
+#define fcloseall _fcloseall
+#define fcvt      _fcvt
+#define fdopen    _fdopen
+#define fileno    _fileno
+#define gcvt      _gcvt
+#define getcwd    _getcwd
+#define getpid    _getpid
+#define getw      _getw
+#define isatty    _isatty
+#define j0        _j0
+#define j1        _j1
+#define jn        _jn
+#define lfind     _lfind
+#define lsearch   _lsearch
+#define lseek     _lseek
+#define memccpy   _memccpy
+#define mkdir     _mkdir
+#define mktemp    _mktemp
+#define open      _open
+#define putenv    _putenv
+#define putw      _putw
+#define read      _read
+#define rmdir     _rmdir
+#define strdup    _strdup
+#define swab      _swab
+#define tempnam   _tempnam
+#define tzset     _tzset
+#define umask     _umask
+#define unlink    _unlink
+#define utime     _utime
+#define wcsdup    _wcsdup
+#define write     _write
+#define y0        _y0
+#define y1        _y1
+#define yn        _yn
+#endif
+'
 ])