[X86] Fix LowerAsmOutputForConstraint.

Summary:
Update Flag when generating cc output.

Fixes PR40737.

Reviewers: rnk, nickdesaulniers, craig.topper, spatel

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D58283

llvm-svn: 354163