[MC] [Win64EH] Check for matches between epilogs and the prolog on ARM64

This allows sharing opcodes between prolog and epilog even when there
is more than one epilog.

I didn't make any handcrafted special MC level testcases for this (yet
at least), but it does seem to have the expected effect on two existing
CodeGen level testcases.

Differential Revision: https://reviews.llvm.org/D125619