[llvm] [LegalizeTypes] Use vector CTPOP for wide integer popcount on VPOPCNTDQ targets (PR #182675)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon requested changes to this pull request.

You're very unlikely to be able to avoid regressions trying to do this in legalization, as I said previously you need to try to do this inside ReplaceNodeResults

Also, I've pushed #182676 to provide baseline non-vlx vpopcntdq test coverage

https://github.com/llvm/llvm-project/pull/182675