[ELF][PPC32] Support range extension thunks with addends

* Generalize the code added in D70637 and D70937. We should eventually remove the EM_MIPS special case.
* Handle R_PPC_LOCAL24PC the same way as R_PPC_REL24.

Reviewed By: Bdragon28

Differential Revision: https://reviews.llvm.org/D73424