Its checking if the PHP $GLOBALS variable exists.
This is something that has always existed in php (and still does).
It looks like they changed its behavior in php 5.4, so its not always initialized straight away, but it should always exist by the time that check runs.
http://php.net/manual/en/reserved.variables.globals.php
Quote:
As of PHP 5.4 $GLOBALS is now initialized just-in-time.
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