[C++11] Modernize the IR library a bit.

No functionality change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203465 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/IR/User.h

@@ -178,8 +178,8 @@ public:
   // delete.
   //
   void dropAllReferences() {
-    for (op_iterator i = op_begin(), e = op_end(); i != e; ++i)
-      i->set(0);
+    for (Use &U : operands())
+      U.set(0);
   }
 
   /// replaceUsesOfWith - Replaces all references to the "From" definition with