Even though we build USD as static, it still feels the need to mark its
symbols with declspec(dllexport) which means the blender binary now exports
now this isn't necessarily harmful there is no reason to be sloppy and
export symbols that have no business getting exported.
This patch fixes the behavior for USD which was by far the worst offender
in this area with 6137 exports. However that doesn't mean the other libs
that exhibit this behavior get a free pass, they too will be dealt with.