forward declare some structs to fix compile errors
forward declare some structs to fix compile errors

airtame/enet,chenbk85/enet,michalslonina/enet,wangscript/enet,alexxvk/enet,nicolaichuk/enet,stiljg/enet,kitech/enet,elliotwhisper/enet,eisenhauer/enet,shumtn/enet,freeminer/enet,airtame/enet,lsalzman/enet,eisenhauer/enet,elliotwhisper/enet,nicolaichuk/enet,chenbk85/enet,freeminer/enet,eisenhauer/enet,shumtn/enet,alexxvk/enet,kitech/enet,wangscript/enet,michalslonina/enet,stiljg/enet