SystemTools: support deleting junction points

Junction points can exist in directories which may be manipulated within
CMake. The problem is that junction points are currently completely
unsupported within CMake. Since junctions need special API calls to
manipulate, DeleteFileW does not work and instead DeviceIoControl must
be used. Token privilege API calls must also be used to be able to
actually open the junction points.

Change-Id: I3e4ff3b7a600146ac3574d2b17890eef07d06496