Fix gstreamer-plugins-bad after changes in the master port
Fix build of gstreamer and gstreamer1 with glib 2.38.x [1]. Update gstreamer and gstreamer-plugins to new rules, USES=gmake pathfix, new LIB_DEPENDS syntax. Only pull in flex if base version is too old. Be more selective for which OSVERSIONS we need gcc due to the clang bug. Obtained from: Gstreamer upstream [1]