configure: turn on all unused warnings by default
configure: turn on all unused warnings by default

Change-Id: I7f6cb446cd3ac57ac39835cf065d9501a66acd5b

ShiftMediaProject/libvpx,mwgoldsmith/vpx,mwgoldsmith/libvpx,mwgoldsmith/libvpx,mwgoldsmith/vpx,webmproject/libvpx,mwgoldsmith/vpx,Topopiccione/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,mwgoldsmith/vpx,mwgoldsmith/libvpx,webmproject/libvpx,Topopiccione/libvpx,webmproject/libvpx,webmproject/libvpx,Topopiccione/libvpx,webmproject/libvpx,mwgoldsmith/libvpx,mwgoldsmith/libvpx,ShiftMediaProject/libvpx,Topopiccione/libvpx,mwgoldsmith/vpx,Topopiccione/libvpx,Topopiccione/libvpx,mwgoldsmith/vpx,ShiftMediaProject/libvpx,mwgoldsmith/libvpx,ShiftMediaProject/libvpx