[llvm] X86: make VBMI2 funnel shifts use VSHLD/VSHRD for const splats (PR #169401)

[Yanzuo Liu via llvm-commits]

zwuis wrote:

> Fixes [#166949].

You can use [this syntax](https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue).

https://github.com/llvm/llvm-project/pull/169401