[llvm] [VectorCombine] foldShuffleOfCastops - handle unary shuffles (PR #160009)

[Chaitanya Koparkar via llvm-commits]

ckoparkar wrote:

The test `llvm/test/Transforms/LoopVectorize/AArch64/epilogue-vectorization-fix-scalar-resume-values.ll` is failing in CI. I merged `main` but the test fails for me locally as well, so I expect this run to fail.

I do think the failure is unrelated to this patch; the test only runs `-passes=loop-vectorize` and not `-passes=vector-combine` and I don't see anything relevant in the debug output.

https://github.com/llvm/llvm-project/pull/160009