https://gcc.gnu.org/bugzilla/show_bug.cgi?id=128429
--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Changed by r15-3859-g63a598deb0c9fc
libstdc++: #ifdef out #pragma GCC system_header
In r15-3714-gd3a7302ec5985a I added -Wsystem-headers to the libstdc++ build
flags to help catch problems in the library. This patch takes a different
approach, of disabling the #pragma system_header unless _GLIBCXX_SYSHDR is
defined. As a result, the testsuites will treat them as non-system-headers
to get better warning coverage during regression testing of both gcc and
libstdc++, not just when building the library.
My rationale for the #ifdef instead of just removing the #pragma is the
three G++ tests that want to test libstdc++ system header behavior, so we
need a way to select it.
This doesn't affect installed libraries, as they get their
system-header status from the lookup path. But testsuite_flags
--build-includes gives -I directives rather than -isystem.
I think this is WONTFIX or even INVALID because it's working as intended.
