git: cdbf91c7a5a5 - stable/15 - bsd.sys.mk: suppress another gcc warning for libc++

The branch stable/15 has been updated by dim:

URL: https://cgit.FreeBSD.org/src/commit/?id=cdbf91c7a5a55ea139593aaf36142e865c26dfc4

commit cdbf91c7a5a55ea139593aaf36142e865c26dfc4
Author:     Dimitry Andric <dim@FreeBSD.org>
AuthorDate: 2026-01-02 20:29:05 +0000
Commit:     Dimitry Andric <dim@FreeBSD.org>
CommitDate: 2026-01-06 12:30:30 +0000

    bsd.sys.mk: suppress another gcc warning for libc++
    
    Similar to base 63d1c3c43690, suppress -Wc++20-extensions for gcc.
    Otherwise libc++ headers will lead to many -Werror warnings, due to our
    use of -Wsystem-headers, which is not officially supported upstream.
    
    MFC after:      3 days
    
    (cherry picked from commit 62a7fdc13ab45b48977424ef77bbc0f11f601e39)
---
 share/mk/bsd.sys.mk | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/share/mk/bsd.sys.mk b/share/mk/bsd.sys.mk
index 50eb04b9fd15..8ca3fd21c616 100644
--- a/share/mk/bsd.sys.mk
+++ b/share/mk/bsd.sys.mk
@@ -241,7 +241,8 @@ CWARNFLAGS+=	-Wno-error=overflow
 .if ${COMPILER_VERSION} >= 120100
 # These warnings are raised by headers in libc++ so are disabled
 # globally for all C++
-CXXWARNFLAGS+=	-Wno-literal-suffix 			\
+CXXWARNFLAGS+=	-Wno-literal-suffix			\
+		-Wno-c++20-extensions			\
 		-Wno-error=unknown-pragmas
 .endif