[llvm] [X86] Improve llvm.get.active.lane.mask codegen (PR #225832)

[via llvm-commits]

Andarwinux wrote:

There may also need some TTI changes to make loop vectorizer to use llvm.get.active.lane.mask for tail folding (-mllvm -tail-folding-policy=prefer-fold-tail) loops? 

https://github.com/llvm/llvm-project/pull/225832