[M3devel] openbsd threading

[Jay K]

If we use -pthread or -lpthread, the call to sigsuspend hangs.
If we don't use -pthread or -lpthread, some tests fail to build.
So I think we are stuck going back to setjmp munging, which is what 5.8.6 does.
Just for OpenBSD. Darwin/amd64 and old FreeBSD can hopefully still use sigaltstack.
Linux, Solaris, Darwin/non-amd64, current FreeBSD can still use get/set/make/swapcontext.
Maybe I'll upgrade to OpenBSD 4.7 first and give that a shot. I'm one version behind, 4.6.

 - Jay