OpenBSD fixes

There is no symbol versioning of libraries on OpenBSD and shared libraries are of the form foo.so.major.minor with no symlinks so dlopen libopenal.so and let ld.so figure it out instead of libopenal.so.1 which doesn't exist.

The other changes remove the linking of -lossaudio which is uneeded with OpenAL and a holdover from the old OSS audio backend.  -pthread can be -lpthread on recent releases of OpenBSD so use that to keep things in sync.

And sync the various flags, changing the "sparc" test to be "sparc64" as all 64 bit capable sparc machines running OpenBSD have a fully 64 bit kernel and userland.