[clang] [clang] Implement __attribute__((format_matches)) (PR #116708)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

High level look... I don't see any huge problems with this.  I'm concerned with teh complexity of the `SemaChecking` changes, that is a huge change for something I don't think needs to be that complicated.  It isn't clear where all the complexity is coming from either.

https://github.com/llvm/llvm-project/pull/116708