[ARM] [Windows] Use COFF stubs for calls to extern_weak functions

As the extern_weak target might be missing, resolving to the absolute
address zero, we can't use the normal direct PC-relative branch
instructions (as that would result in relocations out of range).

Instead check the shouldAssumeDSOLocal method and load the address
from a COFF stub.

This matches what was done for X86 in 6bf108d7.

Differential Revision: https://reviews.llvm.org/D71720