/usr/include/python3.6dm/modsupport.h is in libpython3.6-dbg 3.6.5-3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/include/python3.6dm/../python3.6m/modsupport.h
/usr/include/python3.6dm/../python3.6m/modsupport.h