AddMPIFlags
-----------

Helpers for using MPI from DUNE targets.

.. cmake:command:: add_dune_mpi_flags

  Link the given targets against ``MPI::MPI_C`` and add the compile
  definitions used by DUNE to disable the deprecated MPI C++ bindings.

  DUNE intentionally uses the C MPI interface for C++ targets to avoid ABI
  problems with vendor-specific MPI C++ bindings.

  .. code-block:: cmake

    add_dune_mpi_flags([SOURCE_ONLY] [OBJECT] <target> [<target>...])

  ``SOURCE_ONLY``
    Accepted for compatibility and ignored.

  ``OBJECT``
    Accepted for compatibility and ignored.

  ``targets``
    One or more existing targets to configure.