[gcc r14-5173] libstdc++: use -D_GNU_SOURCE when building libbacktrace

[Ian Lance Taylor <ian@gcc.gnu.org>]

https://gcc.gnu.org/g:2b64e4a54042fb8f75f1c1429eb1c13afb9fa118

commit r14-5173-g2b64e4a54042fb8f75f1c1429eb1c13afb9fa118
Author: Ian Lance Taylor <iant@golang.org>
Date:   Mon Nov 6 15:09:18 2023 -0800

    libstdc++: use -D_GNU_SOURCE when building libbacktrace
    
            PR libbacktrace/111315
            PR libbacktrace/112263
            * acinclude.m4: Set -D_GNU_SOURCE in BACKTRACE_CPPFLAGS and when
            grepping link.h for dl_iterate_phdr.
            * configure: Regenerate.

Diff:
---
 libstdc++-v3/acinclude.m4 | 5 ++++-
 libstdc++-v3/configure    | 5 ++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
index 654b99e92d7..77569d5bb59 100644
--- a/libstdc++-v3/acinclude.m4
+++ b/libstdc++-v3/acinclude.m4
@@ -5443,7 +5443,7 @@ AC_DEFUN([GLIBCXX_ENABLE_BACKTRACE], [
 
   # Most of this is adapted from libsanitizer/configure.ac
 
-  BACKTRACE_CPPFLAGS=
+  BACKTRACE_CPPFLAGS="-D_GNU_SOURCE"
 
   # libbacktrace only needs atomics for int, which we've already tested
   if test "$glibcxx_cv_atomic_int" = "yes"; then
@@ -5471,8 +5471,11 @@ AC_DEFUN([GLIBCXX_ENABLE_BACKTRACE], [
     have_dl_iterate_phdr=no
   else
     # When built as a GCC target library, we can't do a link test.
+    ac_save_CPPFLAGS="$CPPFLAGS"
+    CPPFLAGS="$CPPFLAGS -D_GNU_SOURCE"
     AC_EGREP_HEADER([dl_iterate_phdr], [link.h], [have_dl_iterate_phdr=yes],
 		    [have_dl_iterate_phdr=no])
+    CPPFLAGS="$ac_save_CPPFLAGS"
   fi
   if test "$have_dl_iterate_phdr" = "yes"; then
     BACKTRACE_CPPFLAGS="$BACKTRACE_CPPFLAGS -DHAVE_DL_ITERATE_PHDR=1"
diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure
index a4b12de1f8a..155faf51922 100755
--- a/libstdc++-v3/configure
+++ b/libstdc++-v3/configure
@@ -73299,7 +73299,7 @@ fi
 
   # Most of this is adapted from libsanitizer/configure.ac
 
-  BACKTRACE_CPPFLAGS=
+  BACKTRACE_CPPFLAGS="-D_GNU_SOURCE"
 
   # libbacktrace only needs atomics for int, which we've already tested
   if test "$glibcxx_cv_atomic_int" = "yes"; then
@@ -73382,6 +73382,8 @@ done
     have_dl_iterate_phdr=no
   else
     # When built as a GCC target library, we can't do a link test.
+    ac_save_CPPFLAGS="$CPPFLAGS"
+    CPPFLAGS="$CPPFLAGS -D_GNU_SOURCE"
     cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 #include <link.h>
@@ -73395,6 +73397,7 @@ else
 fi
 rm -f conftest*
 
+    CPPFLAGS="$ac_save_CPPFLAGS"
   fi
   if test "$have_dl_iterate_phdr" = "yes"; then
     BACKTRACE_CPPFLAGS="$BACKTRACE_CPPFLAGS -DHAVE_DL_ITERATE_PHDR=1"