Add a default Index for VTTI::getShuffleCost

When Kind == (Broadcast or Reverse) then Index is not used; make it an optional parameter.

No functionality change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171447 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/TargetTransformInfo.h

@@ -173,7 +173,7 @@ public:
   /// The index parameter is used by some of the shuffle kinds to add
   /// additional information.
   virtual unsigned getShuffleCost(ShuffleKind Kind, Type *Tp,
-                                  int Index) const {
+                                  int Index = 0) const {
     return 1;
   }