Make TreePattern::error use Twine

The underlying error function already uses a Twine,
and most of the uses build up strings.

llvm-svn: 221740

llvm/utils/TableGen/CodeGenDAGPatterns.cpp

@@ -1908,7 +1908,7 @@ TreePattern::TreePattern(Record *TheRec, TreePatternNode *Pat, bool isInput,
   Trees.push_back(Pat);
 }
 
-void TreePattern::error(const std::string &Msg) {
+void TreePattern::error(const Twine &Msg) {
   if (HasError)
     return;
   dump();

llvm/utils/TableGen/CodeGenDAGPatterns.h

@@ -597,7 +597,7 @@ public:
 
   /// error - If this is the first error in the current resolution step,
   /// print it and set the error flag.  Otherwise, continue silently.
-  void error(const std::string &Msg);
+  void error(const Twine &Msg);
   bool hasError() const {
     return HasError;
   }