[clang] [Clang] [Parser] Fixing all callers of `ParseExternalDeclaration` that didn't parse gnu attributes (PR #117148)

[Erich Keane via cfe-commits]

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

My only concern is the OpenMP stuff, but if @alexey-bataev is ok with it, so am I.

https://github.com/llvm/llvm-project/pull/117148