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/libtime.cpp

@@ -68,5 +68,5 @@ const luaL_Reg timelib[] = {
     {"utc_time", lua::wrap<l_utc_time>},
     {"utc_offset", lua::wrap<l_utc_offset>},
     {"local_time", lua::wrap<l_local_time>},
-    {NULL, NULL}
+    {nullptr, nullptr}
 };