Use std::string instead of StringRef in ClangAttrEmitter.cpp; per report on

cfe-dev, fixes an error compiling with MSVC.  Using a StringRef here doesn't
look safe in any case.

llvm-svn: 111513

llvm/utils/TableGen/ClangAttrEmitter.cpp

@@ -355,7 +355,7 @@ namespace {
   };
 
   class EnumArgument : public Argument {
-    StringRef type;
+    std::string type;
     std::vector<StringRef> values, enums;
   public:
     EnumArgument(Record &Arg, StringRef Attr)