[gcc r16-7115] libstdc++: Default to C++20 in src/experimental/Makefile.am

[Jonathan Wakely]

https://gcc.gnu.org/g:833cbd870f05e0d7fa38cb5cf60a9effea6582bb

commit r16-7115-g833cbd870f05e0d7fa38cb5cf60a9effea6582bb
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Jan 28 10:27:07 2026 +0000

    libstdc++: Default to C++20 in src/experimental/Makefile.am
    
    r16-7089-gfbde291af66e02 had a stray change to the Makefile.in but
    actually we probably should change that directory to use C++20, now that
    it's the default. So this updates the Makefile.am, and the Makefile.in
    doesn't need to be regenerated now.
    
    libstdc++-v3/ChangeLog:
    
            * src/experimental/Makefile.am: Change AM_CXXFLAGS to use C++20
            by default.

Diff:
---
 libstdc++-v3/src/experimental/Makefile.am | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libstdc++-v3/src/experimental/Makefile.am b/libstdc++-v3/src/experimental/Makefile.am
index e428aef23c04..bad10b40e21d 100644
--- a/libstdc++-v3/src/experimental/Makefile.am
+++ b/libstdc++-v3/src/experimental/Makefile.am
@@ -67,7 +67,7 @@ libstdc__exp_la_DEPENDENCIES = \
 # OPTIMIZE_CXXFLAGS on the compile line so that -O2 can be overridden
 # as the occasion calls for it.
 AM_CXXFLAGS = \
-	-std=gnu++17 -nostdinc++ \
+	-std=gnu++20 -nostdinc++ \
 	$(glibcxx_lt_pic_flag) $(glibcxx_compiler_shared_flag) \
 	$(XTEMPLATE_FLAGS) $(VTV_CXXFLAGS) \
 	$(WARN_CXXFLAGS) $(OPTIMIZE_CXXFLAGS) $(CONFIG_CXXFLAGS) \