There appears to be a setup bug in c30 and c31 releases that omits the proper library references from Makefile_gnu when the 'X' option is used with install.com. The symptom is a lengthy list of undefined globals, many with the letter 'x' as the first char of the name. The workaround is to edit build/gnu/Makefile_gnu, and change line 10
to include the library ref as
GLIB = -L/usr/X11R6/lib -lX11
and then re-run install.com; the final 'link and load' step should now succeed. It is not necessary to re-compile.
A distribution fix for build/UNX/Makefile_gnu has been posted in the "Bug fix" forum.