https://trac.macports.org/ticket/60039
Sadly, it still took me a bit to sort it out. You need python2.7 and boost.
sudo port select python27
If you do not have python27, install it. (however, it'll probably come with boost)
sudo port install boost @no_single+no_static+python27
At this point, you should be able to build FreeCad
sudo port install freecad
