[AArch64][WinCFI] Do not pair callee-save instructions in LoadStoreOptimizer

Prevent the LoadStoreOptimizer from pairing any load/store instructions with
instructions from the prologue/epilogue if the CFI information has encoded the
operations as separate instructions.  This would otherwise lead to a mismatch
of the actual prologue size from the size as recorded in the Windows CFI.

Reviewers: efriedma, mstorsjo, ssijaric

Reviewed By: efriedma

Differential Revision: https://reviews.llvm.org/D65817

llvm-svn: 368164