-Waggregate-return: used by some Qt clases extensively and not super
useful for this example. Supress it.
warning: "GL_GLEXT_VERSION" redefined: Perform the same workaround as
qmlglsink by defining the old gl/GL.h header guard if the new GL/gl.h
guard exists.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/-/merge_requests/752>
gstgl doesn't undo/overwrite what GL state the examples are changing
anymore. As such, the examples need to reset the GL state themselves
to be able to play nice with libgstgl