If $wgMainCacheType = CACHE_ACCEL, but there is no APC, then its
possible that CACHE_ANYTHING will default to CACHE_NONE because
that's what CACHE_ACCEL would do.
Possibly also T147161
Bug: T160519
Change-Id: I9ac2d071437b35a0f9cd3678e2279628f7b1931e