The first thing I tried was make the main Makefile include 'freebsd.mk', but some files still wouldn't compile.
As a result, I removed socket/recvfd2.c and socket/sendfd2.c from the build because OpenBSD does not support SO_PEERCRED. It provides getpeereid(2), which I will look up later.
Next, OpenBSD doesn't provide the POSIX.2001 pseudo-terminal functions grantpt(), ptyname(), posix_openpt(), unlockpt... a bit of googling brought up this short thread:
http://marc.theaimsgroup.com/?l=netbsd-tech-kern&m=108534411826666&w=2
After reading it, I gather that not providing those functions is a good thing: one less suid binary in the system. Better yet, the same functionality it still provided by OpenBSD, Quoting from same post:
OpenBSD implemented a different (better) way of doing this, by adding
/dev/ptm, and getting the master, slave fd's and the master and slave
names through an ioctl(3), doing the chown/chmod's in the process.
The posix way, requires a userland setuid program ``pt_chown'' to do
the nasty chown job, which is called from grantpt(3).
