[IPO] Use default member initialization (NFC)

Identified with modernize-use-default-member-init.

Author: kazutakahirata

llvm/lib/Transforms/IPO/CalledValuePropagation.cpp

@@ -70,7 +70,7 @@ class CVPLatticeVal {
     }
   };
 
-  CVPLatticeVal() : LatticeState(Undefined) {}
+  CVPLatticeVal() = default;
   CVPLatticeVal(CVPLatticeStateTy LatticeState) : LatticeState(LatticeState) {}
   CVPLatticeVal(std::vector<Function *> &&Functions)
       : LatticeState(FunctionSet), Functions(std::move(Functions)) {
@@ -96,7 +96,7 @@ class CVPLatticeVal {
 
 private:
   /// Holds the state this lattice value is in.
-  CVPLatticeStateTy LatticeState;
+  CVPLatticeStateTy LatticeState = Undefined;
 
   /// Holds functions indicating the possible targets of call sites. This set
   /// is empty for lattice values in the undefined, overdefined, and untracked