Blacklist inter-process communication of unpicklables

Author: rotu

colcon_core/package_identification/python.py

@@ -159,6 +159,8 @@ def _get_setup_result_target(setup_py: str, env: Optional[dict], conn_send):
                 and not callable(value)
                 # Private properties
                 and not attr.startswith('_')
+                # Objects that are generally not picklable
+                and attr not in ('cmdclass', 'distclass', 'ext_modules')
             )})
     except BaseException:
         conn_send.send(traceback.format_exc())