Unconditionally import vtkParallelMPIModule.h

There is no need to do this *only* if USE_STDARG is not defined and in
fact leads to compiler errors if USE_STDARG is defined because
VTKPARALLELMPI_EXPORT does not get defined.

Parallel/MPI/vtkMPI.h

@@ -19,13 +19,13 @@
 
 #ifndef USE_STDARG
 #define USE_STDARG
-#include "vtkParallelMPIModule.h" // For export macro
 #include "vtk_mpi.h"
 #undef USE_STDARG
 #else
 #include "vtk_mpi.h"
 #endif
 
+#include "vtkParallelMPIModule.h" // For export macro
 #include "vtkSystemIncludes.h"
 
 class VTKPARALLELMPI_EXPORT vtkMPICommunicatorOpaqueComm