I will (re)check that everything still builds on Ubuntu later today.

EDIT: Made a couple of small fixes, and now Linux build works. I still don't have sound, but that seems to be a long-standing problem.

@everyone else: if you are using Windows with MinGW, or Mac OS X, or some other platform, and care about being able to build the source in the near future, please speak up. We will drop official support for platforms lacking developers actively interested in supporting that platform.