[clang] [llvm] [Sema] Implement support for -Wformat-signedness (PR #74440)

[Yingchi Long via cfe-commits]

https://github.com/inclyc commented:

Also please add release notes to let users know what has been changed :)

See: `clang/docs/ReleaseNotes.rst`

https://github.com/llvm/llvm-project/pull/74440