[llvm] [WebAssembly] Add support for avgr_u in loops (PR #153252)

[Jasmine Tang via llvm-commits]

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badumbatish wrote:

can confirm this does work, thank you Luke!
<img width="1188" height="488" alt="Screenshot 2025-08-21 at 10 33 47 AM" src="https://github.com/user-attachments/assets/254d6e2d-1fc1-40ab-b1db-b26e4cd9d68b" />


https://github.com/llvm/llvm-project/pull/153252