[llvm] [SimplifyCFG] Don't use a mask for lookup tables generated from switches with an unreachable default case (PR #94468)

[via llvm-commits]

DaMatrix wrote:

https://github.com/llvm/llvm-project/pull/94468#discussion_r1630381209 I like `AllHolesAreUndefined`, have changed it to that.

https://github.com/llvm/llvm-project/pull/94468#discussion_r1630383915 Yeah, I'm definitely interested in doing that, I'll get working on that as soon as this is merged. @DianQK 

https://github.com/llvm/llvm-project/pull/94468