As of today I am successfully compiling Polycode and a Polycode app using a mingw crosscompiler hosted on my mac. It did require some changes to both the cmake scripts and the code.
I submitted the changes back to Polycode here: https://github.com/ivansafrin/Polycode/pull/84
The fork I'm working out of (with other patches) is here: https://bitbucket.org/runhello/polycode
The project I'm building against this is at https://bitbucket.org/runhello/nauts
Assuming you're on Windows, building this should look like:
hg clone https://bitbucket.org/runhello/nauts
./manage.py load -b -d --no-tools --bindings-only
If you're compiling from a mac, you'll need also to set up a toolchain file.
If you can run MSVC, running MSVC would be significantly simpler than trying to run my experimental code linked above. But, mingw is definitely an option.