more missing sstream headers

vtkm/cont/VariantArrayHandle.h

@@ -25,6 +25,8 @@
 #include <vtkm/cont/UncertainArrayHandle.h>
 #include <vtkm/cont/UnknownArrayHandle.h>
 
+#include <sstream>
+
 #ifndef VTKM_NO_DEPRECATED_VIRTUAL
 #include <vtkm/cont/ArrayHandleVirtual.h>
 #endif //VTKM_NO_DEPRECATED_VIRTUAL

vtkm/io/VTKDataSetWriter.cxx

@@ -29,6 +29,7 @@
 #include <fstream>
 #include <iomanip>
 #include <iostream>
+#include <sstream>
 #include <string>
 #include <vector>