[lld-macho] Check for arch compatibility when loading ObjFiles and TBDs

The silent failures had confused me a few times.

I haven't added a similar check for platform yet as we don't yet have logic to
infer the platform automatically, and so adding that check would require
updating dozens of test files.

Reviewed By: #lld-macho, thakis, alexshap

Differential Revision: https://reviews.llvm.org/D97209