[llvm] [Reg2Mem] Add legacy pass wrapping Reg2Mem (PR #111024)

[Nathan Gauër via llvm-commits]

Keenuts wrote:

Hi! Here is some additional context on where we plan on using Reg2Mem pass if you need:
https://github.com/llvm/llvm-project/pull/111026

https://github.com/llvm/llvm-project/pull/111024