Which *nix ? BSD : System V

[John Nelson]

As an alternative to including <sys/ioctl.h>, here is something that works
MUCH BETTER.

Include <signal.h>.  V7 systems do not have any signal which indicates a
child process has terminated.  Both SIII and SV call that signal SIGCLD.
All berkeley systems have an equivalent signal, but call it SIGCHLD.

<signal.h> has other goodies for system differention.  I always use SIGSTOP
to check for job control, and SIGVTALRM for 4.2 BSD exclusivity.