[VPlan] Turn classes with all public members into structs (NFC).

[fhahn]

Summary

struct should be used when all members are public:
https://llvm.org/docs/CodingStandards.html#use-of-class-and-struct-keywords

llvm/lib/Transforms/Vectorize/VPlanTransforms.h

 #define LLVM_TRANSFORMS_VECTORIZE_VPLANTRANSFORMS_H
 
 #include "VPlan.h"
 #include "llvm/IR/Instruction.h"
 #include "llvm/Transforms/Vectorize/LoopVectorizationLegality.h"
 
 namespace llvm {
 
-class VPlanTransforms {
-
-public:
+struct VPlanTransforms {
   /// Replaces the VPInstructions in \p Plan with corresponding
   /// widen recipes.
   static void VPInstructionsToVPRecipes(
       Loop *OrigLoop, VPlanPtr &Plan,
       LoopVectorizationLegality::InductionList &Inductions,
       SmallPtrSetImpl<Instruction *> &DeadInstructions);
 };
 
 } // namespace llvm
 
 #endif // LLVM_TRANSFORMS_VECTORIZE_VPLANTRANSFORMS_H

llvm/lib/Transforms/Vectorize/VPlanValue.h

 class VPSlotTracker;
 
 // This is the base class of the VPlan Def/Use graph, used for modeling the data
 // flow into, within and out of the VPlan. VPValues can stand for live-ins
 // coming from the input IR, instructions which VPlan will generate if executed
 // and live-outs which the VPlan will need to fix accordingly.
 class VPValue {
   friend class VPBuilder;
-  friend class VPlanTransforms;
+  friend struct VPlanTransforms;
   friend class VPBasicBlock;
   friend class VPInterleavedAccessInfo;
   friend class VPSlotTracker;
 
   const unsigned char SubclassID; ///< Subclass identifier (for isa/dyn_cast).
 
   SmallVector<VPUser *, 1> Users;
 

llvm/lib/Transforms/Vectorize/VPlanVerifier.h

 
 #ifndef LLVM_TRANSFORMS_VECTORIZE_VPLANVERIFIER_H
 #define LLVM_TRANSFORMS_VECTORIZE_VPLANVERIFIER_H
 
 #include "VPlan.h"
 
 namespace llvm {
 
-/// Class with utility functions that can be used to check the consistency and
+/// Struct with utility functions that can be used to check the consistency and
 /// invariants of a VPlan, including the components of its H-CFG.
-class VPlanVerifier {
-public:
+struct VPlanVerifier {
   /// Verify the invariants of the H-CFG starting from \p TopRegion. The
   /// verification process comprises the following steps:
   /// 1. Region/Block verification: Check the Region/Block verification
   /// invariants for every region in the H-CFG.
   void verifyHierarchicalCFG(const VPRegionBlock *TopRegion) const;
 };
 } // namespace llvm
 
 #endif //LLVM_TRANSFORMS_VECTORIZE_VPLANVERIFIER_H