[clang] Support `guarded_by` attribute and related attributes inside C structs and support late parsing them (PR #95455)

[Dan Liew via cfe-commits]

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

@pdherbemont Thanks for working on this LGTM. Please confirm that the comments that @aaronpuchert have been added because I couldn't see them.

Once you've done that we can get this merged :) 

https://github.com/llvm/llvm-project/pull/95455