message: Fix include paths when building with external protobuf
diff: @@ -50,7 +50,8 @@ else()
  add_library(libprotobuf UNKNOWN IMPORTED)
  set_target_properties(libprotobuf PROPERTIES
  IMPORTED_LOCATION "${Protobuf_LIBRARY}"
  - INTERFACE_INCLUDE_SYSTEM_DIRECTORIES "${Protobuf_INCLUDE_DIR}"
  + INTERFACE_INCLUDE_DIRECTORIES "${Protobuf_INCLUDE_DIR}"
  + INTERFACE_SYSTEM_INCLUDE_DIRECTORIES "${Protobuf_INCLUDE_DIR}"
  )
  get_protobuf_version(Protobuf_VERSION "${Protobuf_INCLUDE_DIR}")
  endif()
  