[clang] [Clang] Fix __cpuidex conflict with other offloading targets (PR #157741)

[Aiden Grossman via cfe-commits]

https://github.com/boomanaiden154 approved this pull request.

Seems reasonable enough to me. I might try a more principled fix in `clang/lib/Basic/Builtins.cpp` again at some point, but that needs some more thinking and this works well for now.

https://github.com/llvm/llvm-project/pull/157741