[llvm-branch-commits] [NFC] [MTE] simplify tagp logic (PR #110337)

[Florian Mayer via llvm-branch-commits]

https://github.com/fmayer created https://github.com/llvm/llvm-project/pull/110337

We would put a placeholder in the tagp instruction, then replace all
uses of the original alloca with this, then replace the placeholder.

We use replaceUsesWithIf anyway, so it's easier to understand if we just
exclude the tagp call there.