Mark LWG#2260 as complete. We already did the right thing, so I just added tests to ensure that we continue to DTRT.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@338936 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/utilities/memory/pointer.traits/pointer.traits.functions/pointer_to.pass.cpp

@@ -39,6 +39,7 @@ int main()
 {
     {
         int i = 0;
+        static_assert((std::is_same<A<int>, decltype(std::pointer_traits<A<int> >::pointer_to(i))>::value), "");
         A<int> a = std::pointer_traits<A<int> >::pointer_to(i);
         assert(a.t_ == &i);
     }