Relates to https://github.com/llvm/llvm-project/issues/119281
Note:
1) As this PR enables `-Werror` for `libc` tests, it's very likely some
downstream CI's may fail / start failing, so it's very likely this PR
may need to be reverted and re-applied.
P.S.
I do not have merge permissions, so I will need one of the reviews to
merge it for me. Thank you!
Refer: 7.3.1 from [ISO
SPEC](https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3220.pdf)
I have added complex variants of F16 and F128 in libc doc but have
omitted support for them since we will have to first investigate how
their support matrix for clang and gcc looks like, and then add header
guards for them accordingly. Planning to add them in follow up PRs once
this gets landed.
