[clang] [clang][modules] Print library module manifest path. (PR #76451)

[Fangrui Song via cfe-commits]

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

LGTM with a few nits. Can you double check modules.json is inside `lib/` (`usr/lib/x86_64-linux-gnu{{/|\\}}modules.json`) instead of some directory under `include`?

https://github.com/llvm/llvm-project/pull/76451