The patch at URL enables compiling on OpenBSD. Makefile and q_platform.h are based on the FreeBSD version.
The code is excellent. I didn't have to patch anything else than trivial things to get it working. QVM doesn't work as there are some security limitations in OpenBSD that prevents it.
OpenBSD's SDL doesn't have a working SDL_LoadObject() implementation so I had to add OpenBSD to the dedicated ifdef in sys_loadlib.h.
Probably it will work on other archs than i386 but I don't have the hardware to test it so the patch doesn't have them enabled.
And when you remember there is no OpenGL acceleration available on OpenBSD... wait and see ;)
Created attachment 1538 [details] OpenBSD patch Added the patch itself.