fix warnings (#648)

* fix unknown command line argument

* fix warnings settings for gcc

* fix -Wzero-as-null-pointer-constant

* revert CMakeLists.txt

src/logic/scripting/lua/libs/libweather.cpp

@@ -64,5 +64,5 @@ const luaL_Reg weatherlib[] = {
     {"get_current_data", lua::wrap<l_get_current_data>},
     {"get_fall_intensity", lua::wrap<l_get_fall_intensity>},
     {"is_transition", lua::wrap<l_is_transition>},
-    {NULL, NULL}
+    {nullptr, nullptr}
 };