[llvm] [clang] [PowerPC][X86] Make cpu id builtins target independent and lower for PPC (PR #68919)

[Amy Kwan via llvm-commits]

https://github.com/amy-kwan approved this pull request.

I meant to approve this before but forgot. I think LGTM once the comments are addressed.

https://github.com/llvm/llvm-project/pull/68919