Apparently GLFW has a habit of not working on Wayland, because they
hard-code the platform at compile time. Might as well just provide all
four variants, who really cares about a few extra binaries?

The proper solution would be to make loading the windowing system
dynamic at runtime, but that probably requires handling command line
arguments and I can't really be bothered.

Also suppress a warning in the sdl code by rewriting it slightly.