Mark lvDoNotEnregister lclVars as contained

Mark lvDoNotEnregister lclVars as contained

Even if a lclVar is tracked, it may not be a register candidate. When determining whether a lclVar should be contained or RegOptional, take that into account.
In the interest of making this as accurate as possible, mark lclVars early as lvDoNotEnregister when they meet criteria that will later disqualify them from a register.