fatal-signal: Initialize library upon any call to public function.

fatal-signal: Initialize library upon any call to public function.

Not calling fatal_signal_init() means that the signal handlers don't get
registered, so the process won't clean up on fatal signals.  Furthermore,
signal_fds[0] is then 0, which means that fatal-signal_wait() waits on
stdin, so if you are testing a program interactively and accidentally type
something on stdin then that program's CPU usage jumps to 100%.

Since poll_block() calls fatal_signal_wait() this seems like the most
reliable solution.