[clang] [Clang] Emit a diagnostic note at the class declaration when the method definition does not match any declaration. (PR #110638)

[Haojian Wu via cfe-commits]

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

Thanks, the change looks good to me.

Please also add a note in the `clang/docs/ReleaseNotes.rst`


https://github.com/llvm/llvm-project/pull/110638