I did some experiments with autoconf but I had no luck in getting it right on BSDish platforms. I ran out of free time, too. Jesse was going to work on the matter at PyCon anyway so I stopped pursuing the failing tests. It's no fun debugging these kind of problems through the build bots. I'm looking forward in getting access to the snakebit network. It will make our work much easier."I guess multiprocessing doesn't use autoconf tests for historical reasons. It's ancestor -- the pyprocessing package -- was using hard coded values, too." [quoting myself]
Anyway, it turned out that platforms FreeBSD and Darwin are having known bugs like a broken sem_getvalue() function. Jesse and Martin von Löwis have finished their combined work. I'll release a new version of the multiprocessing backport when the tests have passed on all releveant build bots.
Good work, Jesse and Martin!