Provided overload to TypeClass::builtinTypeInfo to return true.

Shouldn't almost all types have a builtin typeinfo? Maybe it'd be better to
have the default at true and only overload typedef and friends.

dmd/mtype.h

@@ -640,6 +640,7 @@ struct TypeClass : Type
     int checkBoolean();
     TypeInfoDeclaration *getTypeInfoDeclaration();
     int hasPointers();
+    int builtinTypeInfo();
 
     type *toCtype();