The ebuild for version 1.10 added gnome-shell as a strict requirement, which the 1.9.4-r1 ebuild did not have. I created a local copy of the ebuild file and removed the dependency and the application compiles works just fine. Please make this optional via an appropriate use flag so it can be used with other environments.
+ 03 Dec 2013; Pacho Ramos <pacho@gentoo.org> workrave-1.10.ebuild: + gnome-shell dependency is not really needed (#493134 by Kevin Bryan) +