[clang] [clang Dependency Scanning] Enhance File Caching Diagnostics (PR #144105)

[Jan Svoboda via cfe-commits]

https://github.com/jansvoboda11 approved this pull request.

LGTM with one nit suggestion. There seems to be a build failure in CI due to revert of @Bigcheese's commit, so that probably needs to be taken care of before merging. I'd also like to see the downstream PR before merging this one just so we know things integrate nicely with the C API.

https://github.com/llvm/llvm-project/pull/144105