The /var/tmp directory is not mounted as tmpfs unlike /tmp which is
mounted as such on some distros like Fedora or Arch. Since there isn't
really a benefit to having the cache on tmpfs, this change should allow
for a larger cache if needed without worrying about running out of RAM.
The current 10 GiB cache size is too large to fit into tmpfs for VMs and
other machines with smaller RAM sizes. Most non-Debian distros mount
/tmp on tmpfs.
