[llvm] [SelectionDAG][x86] Ensure vector reduction optimization (PR #144231)

[Suhajda Tamás via llvm-commits]

sutajo wrote:

I reverted the custom lowering here and moved it to [x86-custom-lower-vecreduce](https://github.com/sutajo/llvm-project/tree/x86-custom-lower-vecreduce)

It is still WIP, I plan to add also xor/or/and and after that I will create a PR.

https://github.com/llvm/llvm-project/pull/144231