[llvm] [LV][CSSPGO] Don't let pseudo probes block early-exit vectorization (PR #220149)

[chandan singh via llvm-commits]

chandankds wrote:

Thanks for the review.

- Retagged the PR as `[LV][CSSPGO]`.
- Documented `llvm.pseudoprobe` in LangRef next to `llvm.sideeffect`.
- Switched the VPlan check to `match(&R, m_Intrinsic<Intrinsic::pseudoprobe>())` instead of inspecting the underlying IR value.

https://github.com/llvm/llvm-project/pull/220149