error out on any error, and ignore two errors that were already ignored (on cross builds w/o qemu)...

[jmg]

Summary

More than once I forgot to buildkernel, and the vm image scrolls
right past the error which you don't find out till you try to boot
the system. Adding set -e fixes that, BUT when cross building, w/o
qemu, a couple commands fail...

newaliases is now a noop since the switch to dma, and ldconfig appears
to be run at start anyways, so not sure why it's needed here...

Test Plan

built amd64 vm on arm64 and it completed w/o error...