[clang] [clang] Fix RecursiveASTVisitor to traverse the exception parameter in ObjCAtCatchStmt. (PR #216125)

[Nico Weber via cfe-commits]

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

Nice find! lgtm

I looked through RAV clients a bit, and this adds a whole bunch of progressions. Most notably, -Wunguarded-availability now finds use of unavailable types in `@catch`. I think this should basically never happen in practice, so it's unlikely to break projects, but maybe worth an addition to clang/test/SemaObjC/unguarded-availability.m and a release note for that (as it could in theory affect -Werror builds).

It should also help several clangd tools, and probably more.

Thanks for the patch!

https://github.com/llvm/llvm-project/pull/216125