Add GCC 11 and C++20 workarounds

GCC 11.1 has a bug [1] in the preprocessor that leads to
-Wsuggest-override warnings being raised in random places, even under
pragmas that are supposed to suppress it. For some reason, NOT using the
integrated preprocessor fixes it, so add that flag as a workaround.

Also, GCC 11 introduces a family of warnings for C++20's deprecations of
mixed enum arithmetic, which we use all over the place. Avoid a hard
error for those warnings.

[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100796

Change-Id: I3b2aefa385f191f207e7eb876bc1ed0b18fb342b
Pick-to: 6.1 6.2
Task-number: QTBUG-93360
Task-number: QTBUG-94059
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

0 files changed, 0 insertions, 0 deletions