Unfortunately, this culprit looks like the fine manual. The example in perlfunc (5.6.0) reads:

use POSIX ":sys_wait_h";
#...
do {
    $kid = waitpid(-1,&WNOHANG);
} until $kid == -1;
[download]

Worse yet, the docs for POSIX in 5.7.2 give this example:

$pid = POSIX::waitpid( -1, &POSIX::WNOHANG );
print "status = ", ($? / 256), "\n";
[download]

You want to submit a doc patch to p5p or should I? :)