Add no_sanitize('hwaddress') (and 'memtag', but that's a no-op).

Currently, `__attribute__((no_sanitize('hwaddress')))` is not possible. Add this piece of plumbing, and now that we properly support copying attributes between an old and a new global variable, add a regression test for the GlobalOpt bug that previously lost the attribute.

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D127544