If building from source use the git repository at
https://github.com/gtownsend/icon
rather than the source download at the Icon web site.
If building the X windows version of Icon, you will need the X11
and Xt development libraries (libx11-dev, libxt-dev
and libxpm-dev packages on Debian based distributions or
libX11-devel, libXt-devel and libXPm-devel on Red Hat
based distributions).