[llvm] [llvm][ScheduleDAG] Set a fixed size for Sched::Preference (PR #94523)

[Jon Roelofs via llvm-commits]

jroelofs wrote:

I have a follow-up patch that puts `Node` and `Instr` into a union & rearranges things a little to bring it down to 256b. I'll post that shortly.

https://github.com/llvm/llvm-project/pull/94523