See PHI36. APCu originally had apc_ methods, but at some point dropped these and only provides apcu_ methods.

When the apcu_ method is present, use it. It may not be present for older versions of APCu, so keep the fallback.

• With modern APCu, clicked "Purge Caches" in Config > Caches.
• Before: fatal on bad apc_clear_caches call.
• After: Valid cache clear.