portmgr@ plans to make python 3.6 default version of python in the next days.
cad/freecad fails to build with DEFAULT_VERSIONS=python=3.x
I'm not sure FreeCAD 0.17 will even work with Python 3 (IIRC full Python 3 support was on the roadmap for 0.18).
If it's urgent, feel free to restrict FreeCAD to Python 2 - I cannot look into this before end of the week.
A commit references this bug:
Date: Mon Feb 18 17:12:36 UTC 2019
New revision: 493279
Fix build with DEFAULT_VERSIONS=python=3.x