Symfony polyfill backporting apcu_* functions to lower PHP versions

 This component provides `apcu_*` functions and the `APCUIterator` class to
 users of the legacy APC extension.
 .
 The Symfony Polyfill project backports features found in the latest PHP
 versions and provides compatibility layers for some extensions and functions.
 It is intended to be used when portability across PHP versions and extensions
 is desired.
 .
 Symfony is a PHP framework, a set of tools and a development methodology.