Several things broke in the latest PowerMac snapshot:

* The OFCONS kernel doesn't even compile, because of references to
some adb_*() functions from clock.c.

* After hacking around that, for some reason, it simply fails to talk
to my serial console at all.  I don't know why.

* The POWERMAC kernel hangs during configure(), after printing:

  adb0 at obio0 offset 0x16000 irq 18