Two problems:
1) Trying to build a kernel without an rcons device produces lots of
unresolved externals and one compile error in scc.c. I want to build a bare
minimum kernel for use with a serial console, only - no framebuffer support
at all.
2) Trying to boot the machine without a serial connection produces a weird
failure mode: it appears to run correctly, but inetd has a problem that
prevents it from answering any connects at all. When I plug in the console,
with a telnet connection pending, the console shows messages:

Aug  3 20:32:11 elmyra inetd[135]: pmap_set: 100002 2 17 65531: No message
of desired type

The numbers after pmap_set vary, but it's always the same text. inetd hangs
until I log in and su, for some reason; I don't konw whjat that would have
to do with it, but it seems to be the only reliable way to get it loose.
(Rebooting with a console attached would, I would expect.)