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/libbyteutil.cpp

@@ -208,5 +208,5 @@ const luaL_Reg byteutillib[] = {
     {"tpack", lua::wrap<l_tpack>},
     {"unpack", lua::wrap<l_unpack>},
     {"get_size", lua::wrap<l_get_size>},
-    {NULL, NULL}
+    {nullptr, nullptr}
 };