ucontext_tstructure, used in signal handlers, is CPU-specific.
You will need to install a gcc version more recent than 3.3 on your OpenBSD box. Upgrading gcc seems to be a non-trivial affair.
Also, at one time we had testers for Solaris/x86 and Linux/PPC. Not anymore, unfortunately, and recent changes to the runtime and FFI lead me to believe that Factor may no longer work on these platforms. I'm going to test Factor on Linux/PPC before releasing 0.88, but I don't have the time, inclination or hardware to maintain a Solaris/x86 install. If you're interested in seeing support, please post to the mailing list or drop by