[llvm] [CodeGen] Expansion of scalable vector reductions (PR #129214)

[Matt Arsenault via llvm-commits]

arsenm wrote:

I thought we were expanding scalable vector intrinsics in PreISelIntrinsicLowering (e.g. following ab976a17121374ae3407374b2aa6306e95863eb3's example)

https://github.com/llvm/llvm-project/pull/129214