[RFC] Raise the minimum GCC version to GCC 11?

[Florian Weimer]

* H. J. Lu:

> Now we can run glibc tests with the older GCC.   Should we raise the
> minimum GCC version to GCC 11?

Can we ban certain recent GCC extensions, like free label placement (on
declarations and at the end of blocks) and unnamed function parameters?
This would at least ease the backport pain somewhat.

I still need to add a patch to turn on the new GCC 15 warnings as
errors.

We still use GCC 8 to build one of our downstream distributions that see
a substantial amount of backporting.

Moving to something newer than GCC 11 will cause problems for my
workflow because I need to use a glibc 2.34 system to test older release
branches (system libgcc_s and libstdc++ reference glibc 2.35 and later
symbols if system glibc is newer).  It's convenient if the same system
can be used to test the current development branch.

Thanks,
Florian