[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: If933a889e9874b6224713a5d48b3cadd3b66463f
Reviewed-on: https://review.typo3.org/19470
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn