[lld-macho] Implement GOT_LOAD relaxation

We can have GOT_LOAD relocations that reference `__dso_handle`.
However, our binding opcode encoder doesn't support binding to the DSOHandle
symbol. Instead of adding support for that, I decided it would be cleaner to
implement GOT_LOAD relaxation since `__dso_handle`'s location is always
statically known.

Reviewed By: #lld-macho, smeenai

Differential Revision: https://reviews.llvm.org/D86641