ruby-libglade2 is compatible with Ruby 1.9 by now (at least on amd64). Please add 'ruby19' flag. 'ruby19' flag was removed in 2009: 15 Feb 2009; Diego E. PettenГІ <flameeyes@gentoo.org> ruby-libglade2-0.16.0-r1.ebuild: Remove ruby19 from USE_RUBY since it does not build with Ruby 1.9.
I'm closing this bug since ruby-libglade2 is no longer supported upstream and not available in recent versions of ruby-gnome2.