Attach comments to decl even if preproc directives are in between

[alandefreitas]

This issue is dependent on the PR open in the llvm-project: llvm/llvm-project#88367

It refers to its integration in MrDocs once the PR is merged.

This issue is a high priority in Mr. Docs because, without it, most symbols that were originally documented with doxygen in mind cannot be documented.