message: cmake: use system lua if available
diff: +IF (PKG_CONFIG_FOUND)
  + pkg_check_modules(LUA lua>=5.3)
  +ENDIF()
  +IF (NOT LUA_FOUND)
  set(LUA_DIR lua-5.3.4)
  add_library(lua
  @@ -41,3 +45,6 @@ add_library(lua
  target_include_directories(lua INTERFACE
  ${CMAKE_CURRENT_SOURCE_DIR}/${LUA_DIR}/src
  )
  +
  +set(LUA_LIBRARIES lua CACHE INTERNAL "lua implementation" FORCE)
  +ENDIF()
  