Normalize polygon winding order for 3D buildings

The backface culling in rendering those assumes they are all oriented
clockwise, but OSM data doesn't guarantee a specific winding order. This
mostly worked so far as the previously used polygon clipping library ended
up normalizing the winding order as an (unwanted) side-effect. Since that
has been fixed the issue became visible here with building walls sometimes
rendered the wrong way around.


(cherry picked from commit d3c923f7)

(cherry picked from commit c59193e7)