[clang] [Driver] Ignore non-clang pch files when -include a.h probes a.h.gch (PR #69204)

[Michael Spencer via cfe-commits]

Bigcheese wrote:

This incorrectly handles `-gmodules` which produces an object file that contains a clang PCH. Detecting that is a bit harder, is it fine if it just accepts all object files as returned by `llvm::identify_magic`?

https://github.com/llvm/llvm-project/pull/69204