[ModuleInliner] Initialize variables (NFC)

[kazu]

Summary

This patch initializes all class variables in InlineOrder.cpp for
safety just in case we miss them in constructors. Currently, all
these variables are properly initialized in their respective
constructors.

llvm/lib/Analysis/InlineOrder.cpp

SizePriority(const CallBase *CB, FunctionAnalysisManager &,
     Size = Callee->getInstructionCount();
   }
 
   static bool isMoreDesirable(const SizePriority &P1, const SizePriority &P2) {
     return P1.Size < P2.Size;
   }
 
 private:
-  unsigned Size;
+  unsigned Size = UINT_MAX;
 };
 
 class CostPriority {
 public:
   CostPriority() = default;
   CostPriority(const CallBase *CB, FunctionAnalysisManager &FAM,
                const InlineParams &Params) {
     auto IC = getInlineCostWrapper(const_cast<CallBase &>(*CB), FAM, Params);
     if (IC.isVariable())
       Cost = IC.getCost();
     else
       Cost = IC.isNever() ? INT_MAX : INT_MIN;
   }
 
   static bool isMoreDesirable(const CostPriority &P1, const CostPriority &P2) {
     return P1.Cost < P2.Cost;
   }
 
 private:
-  int Cost;
+  int Cost = INT_MAX;
 };
 
 class CostBenefitPriority {
 public:
   CostBenefitPriority() = default;
   CostBenefitPriority(const CallBase *CB, FunctionAnalysisManager &FAM,
                       const InlineParams &Params) {
     auto IC = getInlineCostWrapper(const_cast<CallBase &>(*CB), FAM, Params);
if (P1HasCB || P2HasCB) {
       return LHS.ugt(RHS);
     }
 
     // Remaining call sites are ordered according to their costs.
     return P1.Cost < P2.Cost;
   }
 
 private:
-  int Cost;
-  int StaticBonusApplied;
+  int Cost = INT_MAX;
+  int StaticBonusApplied = 0;
   Optional<CostBenefitPair> CostBenefit;
 };
 
 template <typename PriorityT>
 class PriorityInlineOrder : public InlineOrder<std::pair<CallBase *, int>> {
   using T = std::pair<CallBase *, int>;
 
   bool hasLowerPriority(const CallBase *L, const CallBase *R) const {