USE=livecd causes links to get built in graphical mode, but this fails when libpng is not installed, and libpng is not specified as a dependency. As USE=livecd also implies USE=fbcon then I guess there are also some other missing dependencies. You should add: livecd? ( >=media-libs/libpng-1.2.1 >=media-libs/jpeg-6b sys-libs/gpm ) to RDEPEND
Done, sorry for the wait.