[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: Ia62e06c5fdaab1e836f02020277ca0fb17bf118d
Reviewed-on: https://review.typo3.org/19471
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn