login: structs utmp, utmpx, lastlog _TIME_BITS independence (bug 30701)

These structs describe file formats under /var/log, and should not
depend on the definition of _TIME_BITS.  This is achieved by
defining __WORDSIZE_TIME64_COMPAT32 to 1 on 32-bit ports that
support 32-bit time_t values (where __time_t is 32 bits).

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
(cherry picked from commit 9abdae94)