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.

llvm-svn: 183467
diff --git a/clang/lib/CodeGen/TargetInfo.h b/clang/lib/CodeGen/TargetInfo.h
index b0ddebc..ab7b061 100644
--- a/clang/lib/CodeGen/TargetInfo.h
+++ b/clang/lib/CodeGen/TargetInfo.h
@@ -111,8 +111,13 @@
       return Address;
     }
 
+    /// Corrects the low-level LLVM type for a given constraint and "usual"
+    /// type.
+    ///
+    /// \returns A pointer to a new LLVM type, possibly the same as the original
+    /// on success; 0 on failure.
     virtual llvm::Type* adjustInlineAsmType(CodeGen::CodeGenFunction &CGF,
-                                            StringRef Constraint, 
+                                            StringRef Constraint,
                                             llvm::Type* Ty) const {
       return Ty;
     }