[clang] [llvm] [clang][Driver] Don't ignore -gmodules .gch files (PR #77711)

[Michael Spencer via cfe-commits]

Bigcheese wrote:

Ah, looks like all the other gmodules tests have:
```
// Unsupported on AIX because we don't support the requisite "__clangast"
// section in XCOFF yet.
// UNSUPPORTED: target={{.*}}-aix{{.*}}
```

I'll just add that.

https://github.com/llvm/llvm-project/pull/77711