[llvm] [llvm][Support] Add ARM64e support for split stacks (PR #139964)

[Ahmed Bougacha via llvm-commits]

https://github.com/ahmedbougacha approved this pull request.

There are many situations where this is incorrect, but this seems obscure, will loudly fail, and can easily be fixed as needed, so I think LGTM for arm64e?  We can make it slightly more general with small tweaks on the checks;  suggested inline

cc @asl 

https://github.com/llvm/llvm-project/pull/139964