fork1: FORK_THREAD requires FORK_SHAREFILES
fork1: FORK_THREAD requires FORK_SHAREFILES

Now that file descriptor tables have moved from a per-thread resource
to per-process, it's impossible to fork a thread without sharing the
file descriptor table.

ok guenther

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars