gl: Try GLVND 'opengl' and 'glx' first
This partly fixes building gst-plugins-base on a pure wayland setup.
(Other part is defining
EDIT: Shouldn't be needed anymore thanks to https://github.com/KhronosGroup/EGL-Registry/pull/130EGL_NO_X11
but not sure where to add it cleanly)
Edited by Haelwenn Monnier