Description:
------------
pcntl_waitpid() always returns 0 on php 7.3 but on 7.2 it returns PID of exited child.

Example call: `$pid = pcntl_waitpid($procData['pid'], $status, WNOHANG);`

This is script linked below output on php 7.2.23:

```
/usr/local/Cellar/php@7.2/7.2.23/bin/php script.php
Exiting child 0
unset child 0
```

This is the output on php 7.3.10:

```
/usr/local/Cellar/php/7.3.10/bin/php script.php
Exiting child 0
```


On PHP 7.3 the script never ends and is stuck in infinite while loop because `if ($res === $procData['pid'])` expects PID to be assigned in `$res` on child exit but that never happens.

Test script:
---------------
https://gist.github.com/simPod/5a177947bdf864026bfc59d71d6e9d71