Description:
------------
php 7.4 pcntl_signal not catch SIGCHLD signal.swicth php 5.5 can catch.

Test script:
---------------
<?php
declare(ticks = 1); 

pcntl_signal(SIGCHLD,function($signal){
        echo "get signal $signal";
        pcntl_wait($status);
});



$pid = pcntl_fork();
if($pid == 0){ 
        echo " i am child ".getmypid();
        sleep(1);
        exit();
}

while(1){