/usr/bin/x86_64-linux-gnu-python3.6-config is in libpython3.6-dev 3.6.5-3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/bin/x86_64-linux-gnu-python3.6m-config
/usr/bin/x86_64-linux-gnu-python3.6m-config