Diagnose malformed x86 inline asm using 'y' constraint.

X86's 'y' inline assembly constraint represents an MMX register, this change
prevents Clang from hitting an assertion when passed an incompatible type to
deal with.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@183467 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed