MC: change runtime check to an assertion

It is unclear how it would be possible to get M to be NULL in normal scenarios.
Change this to an assert rather than a runtime check as per dblakie's
suggestion.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204060 91177308-0d34-0410-b5e6-96231b3b80d8

lib/MC/MCParser/AsmParser.cpp

@@ -1998,9 +1998,10 @@ bool AsmParser::parseMacroArguments(const MCAsmMacro *M,
           break;
 
       if (FAI >= NParameters) {
+	assert(M && "expected macro to be defined");
         Error(IDLoc,
               "parameter named '" + FA.Name + "' does not exist for macro '" +
-              (M ? M->Name : "<unnamed>") + "'");
+              M->Name + "'");
         return true;
       }
       PI = FAI;