I reran configure so it would install to a local directory, and then
rebuilt and installed (but no make clean--perhaps I should have said
reconfigure or something like that at the first step?).

There's some confusion about the .so extensions.  It's expecting them
(which seems reasonable), but they aren't there.

When I tried to run:
/usr/local/src/squeak$ ~/staging/bin/squeak SqueakVM &
/usr/local/src/squeak$ could not find display driver vm-display-X11; either:
  - check that /home/ross/staging/lib/squeak/3.8a-2/vm-display-X11.so exists, or
  - use the '-plugins <path>' option to tell me where it is, or
  - remove DISPLAY from your environment.
$ls /home/ross/staging/lib/squeak/3.8a-2/
npsqueak.so  squeak  vm-display-fbdev  vm-display-null  vm-display-X11  vm-sound-NAS  vm-sound-null  vm-sound-OSS
$ gcc --version
gcc (GCC) 3.3.5 (Debian 1:3.3.5-13)
Copyright (C) 2003 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ libtool --version
ltmain.sh (GNU libtool) 1.5.6 (1.1220.2.95 2004/04/11 05:50:42) Debian: 224 $

Copyright (C) 2003  Free Software Foundation, Inc.

Considering the hour, the confusion may be on my part.  But it sort of
looks as if libtool and the makefile aren't interacting well.