boot-time, readutmp: Add a Native Windows boot time fallback.
* lib/boot-time-aux.h (initialize, get_windows_boot_time_fallback): New
functions.
* lib/boot-time.c [_WIN32 && !__CYGWIN__]: Include Windows headers and
<sys/time.h>.
(get_boot_time_uncached): Use the fallback.
* lib/readutmp.c [_WIN32 && !__CYGWIN__]: Include Windows headers and
<sys/time.h>.
(read_utmp_from_file): Use the fallback.
* modules/boot-time (Depends-on): Add gettimeofday.
* modules/readutmp (Depends-on): Add gettimeofday.