[llvm] [ScheduleDAG] Allow disabling the SchedModel / Itineraries during Scheduling (PR #138057)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

I don't know why you would want to only disable this during a specific pass. In general we have too many of these old debug flags used for bringup that have no real use case

https://github.com/llvm/llvm-project/pull/138057