fix AC_CHECK_LIB no longer works with g++ (debian bug#992981)

autoconf.spec

@@ -3,7 +3,7 @@
 
 Name:           autoconf
 Version:        2.71
-Release:        6
+Release:        8
 Summary:        An extensible package to automatically configure software source code packages
 License:        GPLv2+ and GPLv3+ and GFDL-1.3-only
 URL:            https://www.gnu.org/software/%{name}/
@@ -13,6 +13,7 @@ Source2:        autoconf-el.el
 
 Patch1:         backport-_AC_PROG_CXX_STDCXX_EDITION_TRY-fix-typo-in-variable.patch
 Patch2:         backport-Fix-testsuite-failures-with-bash-5.2.patch
+Patch3:         backport-Port-AC_LANG_CALL-C-to-C.patch.patch
 
 Patch9000:      skip-one-test-at-line-1616-of-autotest.patch
 
@@ -73,6 +74,9 @@ fi
 
 
 %changelog
+* Wed Dec 04 2024 Funda Wang <fundawang@yeah.net> - 2.71-8
+- fix AC_CHECK_LIB no longer works with g++ (debian bug#992981)
+
 * Thu Jun 13 2024 fuanan <fuanan3@h-partners.com> - 2.71-6
 - Delete the code that adapts to lib/autoconf/c.m4
 

backport-Port-AC_LANG_CALL-C-to-C.patch.patch

@@ -0,0 +1,36 @@
+From b27bc3e230bb12fdd9a813e38e82bc4c3e22b4cc Mon Sep 17 00:00:00 2001
+From: Paul Eggert <eggert@cs.ucla.edu>
+Date: Tue, 31 Aug 2021 16:30:46 -0700
+Subject: [PATCH] Port AC_LANG_CALL(C) to C++
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+* lib/autoconf/c.m4 (AC_LANG_CALL(C)): Add an extern "C" if C++.
+Problem reported by Vincent Lefèvre (sr #110532).
+---
+ lib/autoconf/c.m4 | 8 +++++++-
+ 1 file changed, 7 insertions(+), 1 deletion(-)
+
+diff --git a/lib/autoconf/c.m4 b/lib/autoconf/c.m4
+index 44443a39..48bd49a3 100644
+--- a/lib/autoconf/c.m4
++++ b/lib/autoconf/c.m4
+@@ -126,7 +126,13 @@ m4_define([AC_LANG_CALL(C)],
+ m4_if([$2], [main], ,
+ [/* Override any GCC internal prototype to avoid an error.
+    Use char because int might match the return type of a GCC
+-   builtin and then its argument prototype would still apply.  */
++   builtin and then its argument prototype would still apply.
++   The 'extern "C"' is for builds by C++ compilers;
++   although this is not generally supported in C code, supporting it here
++   has little cost and some practical benefit (sr 110532).  */
++#ifdef __cplusplus
++extern "C"
++#endif
+ char $2 ();])], [return $2 ();])])
+ 
+ 
+-- 
+2.43.5
+