Fix serial compile error.

vtkm/filter/flow/internal/AdvectAlgorithm.h

@@ -78,6 +78,7 @@ public:
       std::vector<vtkm::Id> ids = this->BoundsMap.FindBlocks(p.GetPosition());
 
       //DRP
+      //Note: For duplicate blocks, this will give the seeds to the rank that first in the list.
       if (!ids.empty())
       {
         auto ranks = this->BoundsMap.FindRank(ids[0]);

vtkm/filter/flow/internal/BoundsMap.h

@@ -310,7 +310,9 @@ private:
       idx += 3;
     }
 
+#ifdef VTKM_ENABLE_MPI
     if (comm.rank() == 0)
+#endif
     {
       std::cout << "BlockBounds: " << this->GlobalBounds << std::endl;
       for (const auto& block : this->BlockBounds)

vtkm/filter/flow/testing/UnitTestStreamlineFilterMPI.cxx

@@ -339,6 +339,7 @@ void TestDuplicatedBlocks(vtkm::Id nPerRank)
   vtkm::FloatDefault dx = x1 - x0;
   vtkm::FloatDefault y0 = 0, y1 = numDims - 1, z0 = 0, z1 = numDims - 1;
 
+  //Create all of the blocks.
   std::vector<vtkm::Bounds> bounds;
   for (vtkm::Id i = 0; i < nPerRank * comm.size(); i++)
   {