Xpetra: Build warnings with GCC 7.2 and CUDA (ATDM build)

Created by: mhoemmen

@trilinos/xpetra

.../Trilinos/packages/xpetra/src/CrsMatrix/Xpetra_TpetraCrsMatrix.hpp(955): warning: missing return statement at end of non-void function "Xpetra::TpetraCrsMatrix<Scalar, int, int, Xpetra::EpetraNode>::getLocalMatrix [with Scalar=double]"
          detected during:
            instantiation of "Xpetra::TpetraCrsMatrix<Scalar, int, int, Xpetra::EpetraNode>::local_matrix_type Xpetra::TpetraCrsMatrix<Scalar, int, int, Xpetra::EpetraNode>::getLocalMatrix() const [with Scalar=double]"
(613): here
            instantiation of "Xpetra::TpetraCrsMatrix<Scalar, int, int, Xpetra::EpetraNode>::TpetraCrsMatrix(const Teuchos::RCP<const Xpetra::Map<int, int, Xpetra::EpetraNode>> &, size_t, Xpetra::ProfileType, const Teuchos::RCP<Teuchos::ParameterList> &) [with Scalar=double]"
.../Trilinos/packages/xpetra/src/CrsMatrix/Xpetra_CrsMatrixFactory.hpp(288): here