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diff --git a/gl/m4/onceonly_2_57.m4 b/gl/m4/onceonly_2_57.m4
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+++ b/gl/m4/onceonly_2_57.m4
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+# onceonly_2_57.m4 serial 4
+dnl Copyright (C) 2002-2003, 2005-2006 Free Software Foundation, Inc.
+dnl This file is free software, distributed under the terms of the GNU
+dnl General Public License.  As a special exception to the GNU General
+dnl Public License, this file may be distributed as part of a program
+dnl that contains a configuration script generated by Autoconf, under
+dnl the same distribution terms as the rest of that program.
+
+dnl This file defines some "once only" variants of standard autoconf macros.
+dnl   AC_CHECK_HEADERS_ONCE          like  AC_CHECK_HEADERS
+dnl   AC_CHECK_FUNCS_ONCE            like  AC_CHECK_FUNCS
+dnl   AC_CHECK_DECLS_ONCE            like  AC_CHECK_DECLS
+dnl   AC_REQUIRE([AC_FUNC_STRCOLL])  like  AC_FUNC_STRCOLL
+dnl The advantage is that the check for each of the headers/functions/decls
+dnl will be put only once into the 'configure' file. It keeps the size of
+dnl the 'configure' file down, and avoids redundant output when 'configure'
+dnl is run.
+dnl The drawback is that the checks cannot be conditionalized. If you write
+dnl   if some_condition; then gl_CHECK_HEADERS(stdlib.h); fi
+dnl inside an AC_DEFUNed function, the gl_CHECK_HEADERS macro call expands to
+dnl empty, and the check will be inserted before the body of the AC_DEFUNed
+dnl function.
+
+dnl This is like onceonly.m4, except that it uses diversions to named sections
+dnl DEFAULTS and INIT_PREPARE in order to check all requested headers at once,
+dnl thus reducing the size of 'configure'. Works with autoconf-2.57. The
+dnl size reduction is ca. 9%.
+
+dnl Autoconf version 2.57 or newer is recommended.
+AC_PREREQ(2.57)
+
+# AC_CHECK_HEADERS_ONCE(HEADER1 HEADER2 ...) is a once-only variant of
+# AC_CHECK_HEADERS(HEADER1 HEADER2 ...).
+AC_DEFUN([AC_CHECK_HEADERS_ONCE], [
+  :
+  AC_FOREACH([gl_HEADER_NAME], [$1], [
+    AC_DEFUN([gl_CHECK_HEADER_]m4_quote(translit(gl_HEADER_NAME,
+                                                 [./-], [___])), [
+      m4_divert_text([INIT_PREPARE],
+        [gl_header_list="$gl_header_list gl_HEADER_NAME"])
+      gl_HEADERS_EXPANSION
+      AH_TEMPLATE(AS_TR_CPP([HAVE_]m4_defn([gl_HEADER_NAME])),
+        [Define to 1 if you have the <]m4_defn([gl_HEADER_NAME])[> header file.])
+    ])
+    AC_REQUIRE([gl_CHECK_HEADER_]m4_quote(translit(gl_HEADER_NAME,
+                                                   [./-], [___])))
+  ])
+])
+m4_define([gl_HEADERS_EXPANSION], [
+  m4_divert_text([DEFAULTS], [gl_header_list=])
+  AC_CHECK_HEADERS([$gl_header_list])
+  m4_define([gl_HEADERS_EXPANSION], [])
+])
+
+# AC_CHECK_FUNCS_ONCE(FUNC1 FUNC2 ...) is a once-only variant of
+# AC_CHECK_FUNCS(FUNC1 FUNC2 ...).
+AC_DEFUN([AC_CHECK_FUNCS_ONCE], [
+  :
+  AC_FOREACH([gl_FUNC_NAME], [$1], [
+    AC_DEFUN([gl_CHECK_FUNC_]m4_defn([gl_FUNC_NAME]), [
+      m4_divert_text([INIT_PREPARE],
+        [gl_func_list="$gl_func_list gl_FUNC_NAME"])
+      gl_FUNCS_EXPANSION
+      AH_TEMPLATE(AS_TR_CPP([HAVE_]m4_defn([gl_FUNC_NAME])),
+        [Define to 1 if you have the `]m4_defn([gl_FUNC_NAME])[' function.])
+    ])
+    AC_REQUIRE([gl_CHECK_FUNC_]m4_defn([gl_FUNC_NAME]))
+  ])
+])
+m4_define([gl_FUNCS_EXPANSION], [
+  m4_divert_text([DEFAULTS], [gl_func_list=])
+  AC_CHECK_FUNCS([$gl_func_list])
+  m4_define([gl_FUNCS_EXPANSION], [])
+])
+
+# AC_CHECK_DECLS_ONCE(DECL1 DECL2 ...) is a once-only variant of
+# AC_CHECK_DECLS(DECL1, DECL2, ...).
+AC_DEFUN([AC_CHECK_DECLS_ONCE], [
+  :
+  AC_FOREACH([gl_DECL_NAME], [$1], [
+    AC_DEFUN([gl_CHECK_DECL_]m4_defn([gl_DECL_NAME]), [
+      AC_CHECK_DECLS(m4_defn([gl_DECL_NAME]))
+    ])
+    AC_REQUIRE([gl_CHECK_DECL_]m4_defn([gl_DECL_NAME]))
+  ])
+])