[gcc r17-1852] libstdc++: Update AC_FOREACH to m4_foreach_w [PR103459]

[Pietro Monteiro]

https://gcc.gnu.org/g:0623f27940353f4cf6da1cccf8a37637a4febecc

commit r17-1852-g0623f27940353f4cf6da1cccf8a37637a4febecc
Author: Pietro Monteiro <pietro@sociotechnical.xyz>
Date:   Thu Jun 25 08:29:18 2026 -0400

    libstdc++: Update AC_FOREACH to m4_foreach_w [PR103459]
    
    AC_FOREACH has been deprecated by Autoconf.  Update to
    m4_foreach_w.  No changes to generated files.
    
            PR bootstrap/103459
    
    libstdc++-v3/ChangeLog:
    
            * configure.ac: Update AC_FOREACH to m4_foreach_w.
    
    Signed-off-by: Pietro Monteiro <pietro@sociotechnical.xyz>

Diff:
---
 libstdc++-v3/configure.ac | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libstdc++-v3/configure.ac b/libstdc++-v3/configure.ac
index c442d068e7a7..db08de7735e4 100644
--- a/libstdc++-v3/configure.ac
+++ b/libstdc++-v3/configure.ac
@@ -802,7 +802,7 @@ AC_CONFIG_FILES([src/libbacktrace/backtrace-supported.h])
 # append it here.  Only modify Makefiles that have just been created.
 #
 # Also, get rid of this simulated-VPATH thing that automake does.
-AC_CONFIG_FILES(AC_FOREACH([DIR], glibcxx_SUBDIRS, [DIR/Makefile ]),
+AC_CONFIG_FILES(m4_foreach_w([DIR], glibcxx_SUBDIRS, [DIR/Makefile ]),
   [cat > vpsed$$ << \_EOF
 s!`test -f '$<' || echo '$(srcdir)/'`!!
 _EOF