This enables clean builds of qtlocation repo even if Qt3D is not available.
In such cases only QtPositioning related projects should be build.

There is a small build fix as well as some quick related includes
changed from proper includes to forward declarations.

Change-Id: Ifa8a9315beabcc1f64be219f8fa55236bf4ce42f
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>