Solve conflicts when including both QtOpenGL headers and resource_provider.h

If resource_provider.h is going to be used to integrate delegated frame
to external compositors, it should avoid conflicting with the system's gl.h.

Change-Id: Ie37d6cde263157e6717cc006a9896f0b9ebdaa5d
Reviewed-by: Zeno Albisser <zeno.albisser@digia.com>