Display arch/hostname on log start

Would be helpful when running a lot of builds on separate machines, or just reading back log files, to have that info. Thinking something like:

>>> kldap: Building user/kldap 22.04.2-r0 (on ppc64 gwyn.foxkit.us using abuild 3.4.2-r2) started Fri, 10 Jun 2022 02:39:45 -0500