make(1) uses sysctlbyname() to find out if it is running on a PC98
machine. This check has been added on 1998/9/9. The MIB variable was
added on 1998/8/31. At that time __FreeBSD_version was 300003. So,
only perform the check *if* __FreeBSD_version is defined and if it's
greater than 300003.
For the record: sysctlbyname was added on 1997/5/30 so this change
automaticly handles that...