[clang] [llvm] [AIX] Lower intrinsic __builtin_cpu_is into AIX platform-specific code. (PR #80069)

[Amy Kwan via llvm-commits]

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

Aside from the comments about updating the assert in `SemaChecking.cpp` and the two comments in `PPCTargetParser.def`, this also LGTM.

https://github.com/llvm/llvm-project/pull/80069