[clang] Mark CWG554 as N/A

P1787: //CWG554 is resolved by using the word “scope” instead of “declarative region”, consistent with its very common use in phrases like “namespace scope”.//

Reviewed By: #clang-language-wg, cor3ntin, aaron.ballman, shafik

Differential Revision: https://reviews.llvm.org/D139172