Update GCC on AT next and apply fixes
Update GCC on AT next and apply fixes

Bump to revision 4546f423ecff

We haven't been able to update GCC on AT next since GCC commit 'ebd5e86c0f4
Improve global state for options', which is causing issues when building
glibc. The issue has already been reported upstream (Bug 100909) [1], but hasn't
been fixed yet. So meanwhile, let's revert it off-tree.

Also, since '6cf0040fff7 libstdc++: Improve std::lock algorithm' gcc_1 fails to
build because libstdc++ tries to call '__gthread_yield' even when we compile
with --disable-threads. A patch has been submitted upstream [2] and has been
approved, but is still waiting to be merged. Meanwhile, apply it off-tree as
well.

[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100909
[2] https://gcc.gnu.org/pipermail/libstdc++/2021-June/052858.html

Signed-off-by: Matheus Castanho <531577e2ea6a1eef9cdabce582a2b074021a1180@linux.ibm.com>

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