[llvm] [X86] Add vXi64 MULHU/MULHS lowering, keeping full-width products scalar (PR #206983)

[Rito Takeuchi via llvm-commits]

Licht-T wrote:

Thanks all! Looks the CI failure doesn't relate to this PR, so the rerun should work.

Once merged, I will create a PR for the cost model.

https://github.com/llvm/llvm-project/pull/206983