cmake: add PLUMED include dir

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

                                               $<$<BOOL:${BUILD_SHARED_LIBS}>:--with-pic>                                                  )

    ExternalProject_get_property(plumed_build INSTALL_DIR)

    set(PLUMED_BUILD_DIR ${INSTALL_DIR})

    set(PLUMED_INSTALL_DIR ${INSTALL_DIR})

    list(APPEND LAMMPS_DEPS plumed_build)

    list(APPEND LAMMPS_LINK_LIBS ${PLUMED_BUILD_DIR}/lib/libplumed.so)

    list(APPEND LAMMPS_LINK_LIBS ${PLUMED_INSTALL_DIR}/lib/libplumed.so)

    set(PLUMED_INCLUDE_DIRS "${PLUMED_INSTALL_DIR}/include/plumed/wrapper")

  else()

    find_package(PkgConfig REQUIRED)

    pkg_check_modules(PLUMED plumed REQUIRED)

    list(APPEND LAMMPS_LINK_LIBS ${PLUMED_LDFLAGS})

    set(PLUMED_INCLUDE_DIRS "${PLUMED_INCLUDE_DIRS}/plumed/wrapper")

  endif()

  include_directories(${PLUMED_INCLUDE_DIRS})

endif()

if(PKG_USER-MOLFILE)