[clang] [clang][Dependency Scanning] Adding an API to Diagnose Invalid Negative Stat Cache Entries (PR #135703)

[Qiongsi Wu via cfe-commits]

qiongsiwu wrote:

Thanks @jansvoboda11 ! The API is updated so that the end result is a vector of paths (strings), so the caller can create the diagnostics. 

I will add the C-API to https://github.com/swiftlang/llvm-project after this PR lands. 

https://github.com/llvm/llvm-project/pull/135703