[Yhc] Mac issues

[Neil Mitchell]

Hi,

I've been trying to debug the mac ppc, which fails with:
src/runtime/BCKernel/thread.c:126: failed assertion `rval==0'

The reason is that sem_init returns -1, to indicate error, and an
error number that indicates ENOSYS: The function sem_init() is not
supported by this implementation.

See http://www.opengroup.org/onlinepubs/007908799/xsh/sem_init.html
for more details.

Of course, I have no idea why sem_init isn't supported, or why its
required for a non-threading example, or anything else - just this
might help someone else debug this error.

Thanks

Neil