[clang] Mark CWG536 as N/A

[[https://wg21.link/p1787 | P1787]]: CWG536 (long partially resolved) is resolved by specifying that unqualified lookup occurs for any kind of unqualified-id as an id-expression.
Wording: An unqualified name is a name that <...>. Unless otherwise specified, such a name undergoes unqualified name lookup from the point where it appears. ([basic.lookup.unqual]/4)

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

Differential Revision: https://reviews.llvm.org/D147564