From the distcc site, describing 2.7.1 changes: "distccmon-gnome now depends only on GTK+ 2.0, not on the GNOME libraries" the ebuild for 2.7.1 has gnome as a dependency, not gtk Reproducible: Always Steps to Reproduce: 1. 2. 3.
See distcc 2.8-r2 instead. Its not wise to backport such changes into stable.