[R21.4] Fix for failure in 21.4 when run by cron

[Stephen J. Turnbull]

RECOMMEND 21.4

Mats Lidell writes:

 > On IRC Aidan suggested further that we should use
 > find_tty_or_stream_console_from_fd from 21.5.
 > 
 > So I tried then just to import that function, use it and from what
 > I find it does seem to work. The assertion does not fire and the
 > compilation is completed with what looks like a good result.
 > 
 > Since I don't know really what I'm doing I'm enclosing the patch
 > below for discussion. Comments?

I don't understand it well myself, but obviously there's a family of
tty_or_stream_console functions, and the find_tty_or_stream_console
function was missing from 21.4, but the others were used in this
context.

Vin, I think it would be good to apply and release this one (without
the bogus hunk from custom-loads, of course).