phantasia: redo how void gets init'd from NetBSD

phantasia: redo how void gets init'd from NetBSD

Change by jmc of NetBSD fame:
    setup now just creates an empty file. When main starts and loads it
    in, it stats and if zero size init's a new location and saves it
    back out. Now games.tgz can be shared among MACHINE_ARCH's

This also makes packaging phantasia easier. Package updates can skip
removing the void file, if it is non-empty.