transfer MPI/OpenMP selection from LAMMPS to downloaded Plumed library configuration

  option(DOWNLOAD_PLUMED "Download Plumed package instead of using an already installed one" OFF)

  if(DOWNLOAD_PLUMED)

    if(BUILD_MPI)

      set(PLUMED_CONFIG_MPI "--enable-mpi")

      set(PLUMED_CONFIG_CC  ${CMAKE_MPI_C_COMPILER})

      set(PLUMED_CONFIG_CXX  ${CMAKE_MPI_CXX_COMPILER})

    else()

      set(PLUMED_CONFIG_MPI "--disable-mpi")

      set(PLUMED_CONFIG_CC  ${CMAKE_C_COMPILER})

      set(PLUMED_CONFIG_CXX  ${CMAKE_CXX_COMPILER})

    endif()

    if(BUILD_OMP)

      set(PLUMED_CONFIG_OMP "--enable-openmp")

    else()

      set(PLUMED_CONFIG_OMP "--disable-openmp")

    endif()

    message(STATUS "PLUMED download requested - we will build our own")

    include(ExternalProject)

    ExternalProject_Add(plumed_build

      CONFIGURE_COMMAND <SOURCE_DIR>/configure --prefix=<INSTALL_DIR>

                                               ${CONFIGURE_REQUEST_PIC}

                                               --enable-modules=all

                                               CXX=${CMAKE_MPI_CXX_COMPILER}

                                               CC=${CMAKE_MPI_C_COMPILER}

                                               ${PLUMED_CONFIG_MPI}

                                               ${PLUMED_CONFIG_OMP}

                                               CXX=${PLUMED_CONFIG_CXX}

                                               CC=${PLUMED_CONFIG_CC}

    )

    ExternalProject_get_property(plumed_build INSTALL_DIR)

    set(PLUMED_INSTALL_DIR ${INSTALL_DIR})