message: Add #ifdef for serial build
diff: @@ -1975,7 +1975,8 @@ BlockILU0::BlockILU0(Operator &op, int block_size_, bool reorder_)
  void BlockILU0::SetOperator(const Operator &op)
  {
  - const SparseMatrix *A;
  + const SparseMatrix *A = NULL;
  +#ifdef MFEM_USE_MPI
  const HypreParMatrix *A_par = dynamic_cast<const HypreParMatrix *>(&op);
  SparseMatrix A_par_diag;
  if (A_par != NULL)
  @@ -1983,7 +1984,8 @@ void BlockILU0::SetOperator(const Operator &op)
  A_par->GetDiag(A_par_diag);
  A = &A_par_diag;
  }
  - else
  +#endif
  + if (A == NULL)
  {
  A = dynamic_cast<const SparseMatrix *>(&op);
  if (A == NULL)
  