PHP 5.5 has apc_ and apcu_. PHP 7 only has apcu_ (without installing apc-bc in pecl. Ugh). HHVM only has apc_
For HHVM supporting apcu_ see https://github.com/facebook/hhvm/issues/6784
For T140587 and https://gerrit.wikimedia.org/r/#/c/299498 I originally just replaced apc_ with apcu_, but for HHVM support, this isn't gonna work.
So, do we create an APCuBagOStuff, and add some if/elseif function_exists in MemoizedCallable as appropriate?
Or, do we "move" everything over to apcu_ calls, and add in GlobalFunctions some wrappers around apc_ per the Compatibility functions?
```
/**
* Compatibility functions
*
* We support PHP 5.5.9 and up.
* Re-implementations of newer functions or functions in non-standard
* PHP extensions may be included here.
*/
```
As is, upgrading to PHP 7 can break login and other stuff if you're trying to use APC, as @Krenair found out... So, it could be suggested our PHP 7 support in REL1_27 is buggy at least