Fix AArch64ConditionOptimizer

Summary:
This pass may modify the Cmp operands. However, the flag reg may be used by both the branch and CSEL.
Modifying CMP will have side effect on CSEL.

Reviewers: t.p.northover

Subscribers: llvm-commits, aemerson, rengolin

Differential Revision: http://reviews.llvm.org/D16147

llvm-svn: 257844