Description:
------------
A backreference to a branch reset group works as expected in PHP 5 but not in PHP 7.

Test script:
---------------
<?php

$string = '--';

$doesNotMatchInPhp7 = '/(?|(---)|(-))\1$/';
$matchesInPhp7 = '/(?|(-)|(---))\1$/';

var_dump(preg_match($doesNotMatchInPhp7, $string));
var_dump(preg_match($matchesInPhp7, $string));