[RFC] Raise the minimum version of GCC for glibc build

[H.J. Lu]

Hi,

Currently, GCC 6 is the minimum version of GCC for glibc build.  But
many ports require a higher version of GCC and GCC 6 won't build
i386 glibc on Fedora 39:

https://sourceware.org/bugzilla/show_bug.cgi?id=31412

Should we raise the minimum version of GCC for glibc build to the
oldest supported GCC release?  The current oldest supported GCC
release is the GCC 11 series.

-- 
H.J.