Note that it's only used for non-pc-relative contexts.
Depends on D79926.
ld64 emits an entry in the rebase table so that the relocation can be adjusted for whatever the final load address ends up being. (I'm assuming it does this for all non-pcrel relocations.) Certainly not something we need to support in this diff, but we should add a TODO.
Ah, it's annoying that endianness means we can't do the usual nice arithmetic checks here :/