[TASK] Detect APC and APCu correctly

APCu is just the user-data part of APC,
providing the same API.

If installed it currently identifies itself
as both "apcu" and "apc" (for compatibility).
Thus if "apcu" shows up, we actually have an APC
without opcache-support.

Resolves: #46821
Releases: 4.5, 4.7, 6.0, 6.1
Change-Id: Ie046fa21102c5c7eb6b5b8a9cf54b20252c30cd9
Reviewed-on: https://review.typo3.org/19462
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn