[llvm] [TableGen] Fix non-deterministic output from emitGetRegClassFromMatchKindFunc. (PR #218560)

[Craig Topper via llvm-commits]

topperc wrote:

> I've gone back and forth on this.
> 
> I think it works, but I also took a look through the history and the programmers guide and saw that people are using MapVector or SortedVectorMap instead. I'm not sure how to decide between these choices.

Maybe I should mention I lifted this from the map in AsmMatcherInfo::buildOperandMatchInfo.

https://github.com/llvm/llvm-project/pull/218560