[X86] Add clang support for X86 flag output parameters.

Summary:
Add frontend support and expected flags for X86 inline assembly flag
parameters.

Reviewers: craig.topper, rnk, echristo

Subscribers: eraman, nickdesaulniers, void, llvm-commits

Differential Revision: https://reviews.llvm.org/D57394

llvm-svn: 354053