[llvm] [X86] Reimplement bundle alignment mode (PR #175830)

[Vitaly Buka via llvm-commits]

https://github.com/vitalybuka approved this pull request.

LGTM with a few nits.

@MaskRay I assume we agree with approach in general. Also this does not introduce changes in existing supported behaviors. We can fix forward feature in the feature relatively easy, if needed.

So would it be more efficient to move forward, and let interested comunity members to deploy the feature and incrementally improve it?

https://github.com/llvm/llvm-project/pull/175830