You access TrinityCore.sln by making it.EDIT: ArcEmu is not entirely different. The base concept is the same for every core archetype.
(Not) recent changes made it so cmake automatically adds every file in folder. Just add them and make them again.
Just follow the instructions and neglect modifying cmakelist.txt.
You CAN add those if you want to add custom scripts for your custom class. E.g. for spells that are not working (yet) or not properly imeplemented, e.g. because of custom mechanics.Ignore that part. You'd create new files for them but they are neglectable if you do not intend to add custom stuff for them just yet.