The "README-EXAMPLES" file for Contiki 2.2.3 says for the "rime" examples to compile, "You will need to have GTK 1.x development libraries installed."

In Ubuntu's Synaptic Package Manager, the package you need is called "libgtk1.2-dev."

"libgtk2.0-dev" doesn't have the gtk-config command line tool.

So far, I see no problem having them both