[AArch64] Async unwind - Adjust unwind info in AArch64LoadStoreOptimizer

[Re-commit after fixing a dereference of "end" iterator]

The AArch64LoadStoreOptimnizer pass may merge a register
increment/decrement with a following memory operation. In doing so, it
may break CFI by moving a stack pointer adjustment past the CFI
instruction that described *that* adjustment.

This patch fixes this issue by moving said CFI instruction after the
merged instruction, where the SP increment/decrement actually takes
place.

Reviewed By: efriedma

Differential Revision: https://reviews.llvm.org/D114547