[llvm] [llvm-exegesis] Add HasNoSchedulingInfo flag to MCInstDesc. (PR #143840)

[Jim Lin via llvm-commits]

tclin914 wrote:

> I also agree that we should probably check if `MCInstrDesc::getSchedClass()` is zero or not instead. Because if I'm not mistaken, you can actually have an instruction that lacks scheduling info without `hasNoSchedulingInfo` being true (as long as `CompleteModel` is false).
> 
> Also, could you add a test?

Done. Thanks.

https://github.com/llvm/llvm-project/pull/143840