this is dependency of korundum, please see the bug dependency chain
Created attachment 196320 [details] kde-base/qtruby-4.2.95.ebuild this works for me ...
note that there exists also dev-ruby/qt4-qtruby ... I was unable to install that (the current version 2.0.3, the one in portage is dead), it does not compile without smoke but it provides some same files that collide
See bug 275941 for details.