the windows builder has 2 different build folders for the debug and release libs, hardcoding the path like this leads to an extra 1GB of downloaded files. The windows builder supplies a single PACKAGE_DIR for both but gets ignored. This change promotes PACKAGE_DIR to be cached in CMakeCache so it can be changed if needed. Differential Revision: https://developer.blender.org/D16213 Reviewed by; brecht, dfelinto