[ms-inline asm] Add a comment.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@163123 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/Mips/AsmParser/MipsAsmParser.cpp

@@ -106,6 +106,9 @@ GetMCInstOperandNum(unsigned Kind, MCInst &Inst,
                     const SmallVectorImpl<MCParsedAsmOperand*> &Operands,
                     unsigned OperandNum) {
   assert (0 && "GetMCInstOperandNum() not supported by the Mips target.");
+  // The Mips backend doesn't currently include the matcher implementation, so
+  // the GetMCInstOperandNumImpl() is undefined.  This is a temporary
+  // work around.
   return 0;
 }