[llvm] [VP] Refactor VectorBuilder to avoid layering violation. NFC (PR #99276)

[Mel Chen via llvm-commits]

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@@ -569,6 +569,9 @@ class VPIntrinsic : public IntrinsicInst {
   /// The llvm.vp.* intrinsics for this instruction Opcode
   static Intrinsic::ID getForOpcode(unsigned OC);
 
+  /// The llvm.vp.reduce.* intrinsics for this intrinsic.
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Mel-Chen wrote:

165f0bcf2dc7bf3f3fe98dc18c3f81e622255a67  Fix the comment.
be39dca2226bff98a292c2542ff884a49c521d14  This commit defined the behavior when passed VP intrinsics. I  define the behavior to return the passed VP intrinsic ID directly. Please let me know if you feel this is unsuitable. 
86f96f1f8a4b4867351f0e5bfc7f7d97c1e889f7 Add round trip tests for `getForIntrinsic`.

https://github.com/llvm/llvm-project/pull/99276