message: add reference to changes
diff: #
  # Based on the pretty-printers for libstdc++.
  -# Copyright (C) 2008-2020 Free Software Foundation, Inc.
  +# Copyright (C) 2008-2021 Free Software Foundation, Inc.
  #
  # This program is free software; you can redistribute it and/or modify
  # it under the terms of the GNU General Public License as published by
  @@ -51,7 +51,8 @@ else:
  _versioned_namespace = '__8::'
  -
  +# new version adapted from https://gcc.gnu.org/pipermail/gcc-cvs/2021-November/356230.html
  +# necessary due to empty class optimization
  def is_specialization_of(x, template_name):
  "Test if a type is a given template instantiation."
  global _versioned_namespace
  