environment/autoconf_cache: switch to off_t=4 for 32bit archs;

Assume that _FILE_OFFSET_BITS=64 is always defined to get proper 64bit support.

Setting it to 8 was giving unexpected results in e2fsprogs, which does not
defined _FILE_OFFSET_BITS=64, and checks for sizeof(off_t) >= sizeof(long long)
to use lseek() rather than lseek64().
e2fsprogs: rebuild with proper off_t size on 32bit archs.