[llvm] [AArch64][GlobalISel] Don't crash when legalising G_*MIN/G_*MAX of pointer vector (PR #168872)

[Nathan Corbyn via llvm-commits]

cofibrant wrote:

> End to end IR tests would be better 

I had planned to use an end to end IR test but unfortunately we still fail to select here so had thought a MIR test would do the job. What would you recommend? 

https://github.com/llvm/llvm-project/pull/168872