Description:
------------
If an undefined unqualified constant is used in a parameter default value and a registered error handler converts the "undefined constant" notice into an exception PHP will hang.

This only happens if global registers are used.

Test script:
---------------
<?php
error_reporting(E_ALL);

function doSomething(string $value = UNDEFINED_XYZ) {
}

set_error_handler(function() {
    throw new Exception;
});

doSomething();

Expected result:
----------------
Exception is thrown

Actual result:
--------------
PHP enters an infinite loop