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)