Remove the explicit SDNodeIterator::operator= in favor of the implicit default

There doesn't seem to be any need to assert that iterator assignment is
between iterators over the same node - if you want to reuse an iterator
variable to iterate another node, that's perfectly acceptable. Just
don't mix comparisons between iterators into disjoint sequences, as
usual.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@231135 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Analysis/CallGraph.h

@@ -104,6 +104,12 @@ class CallGraph {
 
 public:
   CallGraph(Module &M);
+  // Copyable for syntax's sake, but rely on RVO such that this is never called.
+  // Should really make this type legitimately movable instead, possibly my
+  // making FunctionMap values and the CallsExternalCode member unique_ptrs,
+  // then adding some internal helper objects that can call
+  // "allReferencesDropped" on those elements before their final destruction.
+  CallGraph(const CallGraph&); 
   ~CallGraph();
 
   void print(raw_ostream &OS) const;