clients/window: fix build issues w/ gles
clients/window: fix build issues w/ gles

giucam/weston,eyolfson/weston,mchalupa/weston,Gnurou/weston,kwm81/weston,udoprog/weston,Fantu/compositor-spice,krezovic/weston,Gnurou/weston,Fantu/compositor-spice,sir-murray/weston,mchalupa/weston,jonnylamb/weston,jonnylamb/weston,krezovic/weston,giucam/weston,Tarnyko/weston-xdg_surface_present,eyolfson/weston,Fantu/compositor-spice,udoprog/weston,sir-murray/weston,xorgy/weston,xorgy/weston,Tarnyko/weston-xdg_surface_present,kwm81/weston