[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: Id61bcf9277295915a6e204eabab7c65159e98764
Reviewed-on: https://review.typo3.org/19469
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn