message: Support type casting Type to itself
diff: @@ -137,6 +137,9 @@ public:
  template <typename U> U dyn_cast_or_null() const;
  template <typename U> U cast() const;
  + // Support type casting Type to itself.
  + static bool classof(Type) { return true; }
  +
  /// Return the classification for this type.
  unsigned getKind() const;
  