These packages make use of gtk3 useflag which indicates that there are issues of migration to gtk+:3. Gtk3 and similar useflags should be avoided. Adding to tracker. Please have a look.
*librsvg-2.36.0 (12 Apr 2012) 12 Apr 2012; Alexandre Rostovtsev <tetromino@gentoo.org> +librsvg-2.36.0.ebuild, +files/librsvg-2.36.0-rsvg-convert.1.patch, +files/librsvg-2.36.0-rsvg-view-automagic.patch: Version bump with numerous bugfixes. Deprecated /usr/bin/rsvg utility was removed. The rsvg-view-3 utility is now built only when USE="gtk tools".