[llvm] [NFC] add a pre-commit test case for patch #127121 that hoists xxsplitib out of loop (PR #127701)

[Amy Kwan via llvm-commits]

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+;; Test hoisting `xxspltib` out the loop.
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amy-kwan wrote:

Nit; update comment.
```suggestion
;; Test hoisting `xxspltib` out of the loop.
```

https://github.com/llvm/llvm-project/pull/127701