gl-renderer: Compile shaders only when needed
gl-renderer: Compile shaders only when needed

Saves some start up time by not compiling specific shaders until they
are needed.

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