CFG::SuccessorIterator::SuccessorProxy:: Expliictly default copy construction as it is deprecated in C++11 in the presence of explicit copy assignment.

See r231099 for similar issues & details in [Small]BitVector.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@231141 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/IR/CFG.h

@@ -136,6 +136,8 @@ private:
   public:
     explicit SuccessorProxy(const Self &it) : it(it) {}
 
+    SuccessorProxy(const SuccessorProxy&) = default;
+
     SuccessorProxy &operator=(SuccessorProxy r) {
       *this = reference(r);
       return *this;