[llvm] [UTC] Add initial VPlan support. (PR #178534)

[Andrei Elovikov via llvm-commits]

eas wrote:

Unrelated to this PR, but is there a way to autogenerate CHECKs with both `update_test_checks.py` *and* `update_analyze_test_checks.py` for a single file, e.g. https://github.com/llvm/llvm-project/blob/e9677d1554f7cedc0549d6197dd77d76add6be67/llvm/test/Transforms/LoopVectorize/interleave-and-scalarize-only.ll#L3-L4

https://github.com/llvm/llvm-project/pull/178534