GDC CI on MacOS, FreeBSD, Windows

[wjoe]

The approach I took for building, testing and creating a tarball 
for Linux is to build a Docker container which contains enough of 
an installation of the latest Debian with all the dependencies 
necessary to build GDC.

In order to move forward the next targets I want to add are Mac 
OS, FreeBSD, and Windows (but not necessarily in that order) and 
I want to build Docker containers for those like I did for Linux.

Which versions are relevant ?