[llvm] [NFC] clean up memtag-stack code (PR #80906)

[Jeremy Morse via llvm-commits]

jmorse wrote:

I can't comment on the general operation of memory tagging; however IMO you should use `Value::replaceNonMetadataUsesWith` instead of `Value::replaceUsesWithIf`. Metadata uses get deliberately hidden to avoid affecting codegen decisions, and don't appear on the normal use list, so the `isa<DbgVariableIntrinsic>` test will never be true. I think `replaceNonMetadataUsesWith` better expresses what you're aiming for and achieves the same thing.

https://github.com/llvm/llvm-project/pull/80906