[libc] [clang] [Libc] Give more functions restrict qualifiers (PR #78061)

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https://github.com/lntue commented:

LGTM for the libc part.
Thanks for adding the missing qualifiers!  They were specified in our own generated header but not in the implementation: https://github.com/llvm/llvm-project/blob/main/libc/spec/bsd_ext.td#L21

https://github.com/llvm/llvm-project/pull/78061