The fault lies not in our gforth, but in our image_setup. -- William Geekspeare
Thanks, John. That looks like it explains my trouble.
Actually, after my initial post random surfing through the forums led me to
this thread, which deals with the same problem.
Apparently the problem is not with gforth or whatever else is being built, and not that any necessary modules are missing from dev_img, but that the script image_setup.sh that comes with at least versions 1.5 and 1.6 of dev_img fails to create a number of links that are required for ld to find some of the modules.
The thread cited above includes a script that makes up for image_setup.sh's shortcomings. I ran it on my Z and can now successfully build Gforth 0.6.2.