AIX 4.3.2/4.3.3 reports:

$ ./a.out
installing signal handler...
forking...
waiting for child 28312 to exit...
child 28312 has exited
  sig_pid = 28312
  sig_status = 25600
  main_pid = -1
  main_status = 9999
sigchld handler was called before waitpid (no status)
$ 

David

	P.S. Just to protect everyone: This is my own personal response
and does not represent any official statement from IBM Corporation about
the behaviour of any of its software or hardware products.