[llvm] [llvm] Support multiple save/restore points in mir (PR #119357)

[Michael Maitland via llvm-commits]

michaelmaitland wrote:

> @michaelmaitland, do you want me to update this MR, adding information about registers, or should we wait for @preames to leave an opinion?

I thought I responded to this. Sorry. I'd like to see it updated in this PR to avoid the listed concerns.

https://github.com/llvm/llvm-project/pull/119357