CMake: remove BUILD_SHARED_LIBS requirement from PYTHON package

  add_definitions(-DLMP_PYTHON)

  include_directories(${PYTHON_INCLUDE_DIR})

  list(APPEND LAMMPS_LINK_LIBS ${PYTHON_LIBRARY})

  if(BUILD_SHARED_LIBS)

    if(NOT PYTHON_INSTDIR)

      execute_process(COMMAND ${PYTHON_EXECUTABLE}

        -c "import distutils.sysconfig as cg; print(cg.get_python_lib(1,0,prefix='${CMAKE_INSTALL_PREFIX}'))"

        OUTPUT_VARIABLE PYTHON_INSTDIR OUTPUT_STRIP_TRAILING_WHITESPACE)

    endif()

    install(FILES ${CMAKE_CURRENT_SOURCE_DIR}/../python/lammps.py DESTINATION ${PYTHON_INSTDIR})

  if(NOT BUILD_SHARED_LIBS)

    message(FATAL_ERROR "Python package need lammps to be build shared, use -DBUILD_SHARED_LIBS=ON")

  endif()

endif()