lang/gcc12-devel: Update to the 20210912 snapshot of GCC 12.0.0

Add files/patch-gcc-analyzer-bootstrap to fix bootstrap with clang.

Add files/patch-libgfortran-bootstrap to fix bootstrap on i386 and
FreeBSD's idiosyncratic floating point settings.

Temporarily mark BROKEN on amd64 due to an internal error, but
at least give aarch64, i386, and powerpc* the chance to test drive
after we already had to skip another snapshot.