Bug#950137: freecad builds using a fixed python version (3.7)

[Matthias Klose]

Package: src:freecad
Version: 0.18.4+dfsg1-2
Severity: serious
Tags: sid bullseye
User: debian-python at lists.debian.org
Usertags: python3.8

freecad builds using a fixed python version (3.7), but just depends on python3-dev.

That should be fixed by setting PYTHON_CONFIG_SUFFIX in a version agnostic way.
Also note that Python 3.8 drops the m modifier.