package/vlc: depends on the virtual package libgl

Currently, vlc depends on mesa3d to provide the openGL support.

We now have a virtual package, libgl, which ensures openGL is available.

This is support for full OpenGL, which is only available when X.Org is
enabled, which is anyway a dependency of full OpenGL.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Bernd Kuhls <berndkuhls@hotmail.com>
Cc: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>