util/disk_cache: support caches for multiple architectures

util/disk_cache: support caches for multiple architectures

Previously we were deleting the entire cache if a user switched
between 32 and 64 bit applications.

V2: make the check more generic, it should now work with any
platform we are likely to support.

V3: Use suggestion from Emil to make even more generic/fix issue
with __ILP32__ not being declared on gcc for regular 32-bit builds.

Tested-by: Grazvydas Ignotas <notasas@gmail.com>
Tested-by: Dieter Nützel <Dieter@nuetzel-hh.de>