Modernize ipv4.games server

The server was originally written before I implemented support for POSIX
thread cancelation. We now use standard pthreads APIs instead of talking
directly to *NSYNC. This means we're no longer using *NSYNC notes, which
aren't as good as the POSIX thread cancelation support I added to *NSYNC
which was only made possible by making *NSYNC part of libc. I believe it
will solve a crash we observed recently with ipv4.games, courtesy of the
individual who goes by the hacker alias Lambro.

Author: jart