[llvm] [SelectionDAG] Add support for the 3-way comparison intrinsics [US]CMP (PR #91871)

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Poseydon42 wrote:

Thank you for providing the script, I've tested the current revision of the code against the generated tests and it seems to work on both x86_64 and AArch64. I've reduced the maximum size of vector types from 100 to 50 as it was taking ages otherwise, but I don't think it should change anything.

https://github.com/llvm/llvm-project/pull/91871