vtk_jsoncpp.h needs vtkConfigure.h
It is setting the export macro define for jsoncpp based on VTK_BUILD_SHARED_LIBS which is defined in vtkConfigure.h.
Currently on Windows if vtk_jsoncpp is the first vtk header included, linking will fail with duplicate symbols because the export macro is not set right.
@demarle Ideally this should be in 7.1.