[ms-inline asm] Use mnemonicIsValid() in a helpful assert.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@164421 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaStmtAsm.cpp b/lib/Sema/SemaStmtAsm.cpp
index 18616ee..33eb565 100644
--- a/lib/Sema/SemaStmtAsm.cpp
+++ b/lib/Sema/SemaStmtAsm.cpp
@@ -536,6 +536,8 @@
     SmallString<128> OpcodeStr;
     for (unsigned i = 0, e = IDVal.size(); i != e; ++i)
       OpcodeStr.push_back(tolower(IDVal[i]));
+    // FIXME: Convert to a StmtError.
+    assert(TargetParser->mnemonicIsValid(OpcodeStr) && "Invalid mnemonic!");
 
     // Parse the operands.
     llvm::SMLoc IDLoc;