Fix all warnings and remove -Wno-unused-but-set cflag

src/script/lua_api/l_mainmenu.cpp

@@ -1025,10 +1025,6 @@ int ModApiMainMenu::l_download_file(lua_State *L)
 /******************************************************************************/
 int ModApiMainMenu::l_get_video_drivers(lua_State *L)
 {
-	unsigned int index = 1;
-	lua_newtable(L);
-	int top = lua_gettop(L);
-
 	std::vector<irr::video::E_DRIVER_TYPE> drivers
 		= porting::getSupportedVideoDrivers();
 

src/script/lua_api/l_mapgen.h

@@ -23,7 +23,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "lua_api/l_base.h"
 
 class INodeDefManager;
-class NodeResolveInfo;
+struct NodeResolveInfo;
 class DecoSimple;
 class DecoSchematic;