MS asm: Filter out fpsw clobbers

When parsing MS inline assembly, we note that fpsw is an implicit def of
most x87 FP operations, and add it to the clobber list.  However, we
don't recognize fpsw as a gcc register name, and we assert.  Clang
always adds an fpsr clobber, which means the same thing to LLVM, so we
can just use that.

This test case was broken by my LLVM change r196939.

Reviewers: echristo

Differential Revision: http://llvm-reviews.chandlerc.com/D2993