[llvm] [InstCombine] Handle scalable splat in `getFlippedStrictnessPredicateAndConstant` (PR #83980)

[via llvm-commits]

llvmbot wrote:

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Failed to cherry-pick: d51fcd4ed86ac6075c8a25b053c2b66051feaf62

https://github.com/llvm/llvm-project/actions/runs/8156934384

Please manually backport the fix and push it to your github fork.  Once this is done, please create a [pull request](https://github.com/llvm/llvm-project/compare)

https://github.com/llvm/llvm-project/pull/83980