Recommit rL245802: Cleanup fancy pointer rebinding in list using __rebind_pointer.

Currently we need an #ifdef branch every time we use pointer traits to rebind a pointer because
it is done differently in C++11 and C++03. This patch introduces the __rebind_pointer utility to
clean this up.

Also add a test that list and it's iterators can be instantiated with incomplete element types.


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@245806 91177308-0d34-0410-b5e6-96231b3b80d8

include/memory

@@ -932,6 +932,15 @@ public:
         {return _VSTD::addressof(__r);}
 };
 
+template <class _From, class _To>
+struct __rebind_pointer {
+#ifndef _LIBCPP_HAS_NO_TEMPLATE_ALIASES
+    typedef typename pointer_traits<_From>::template rebind<_To>        type;
+#else
+    typedef typename pointer_traits<_From>::template rebind<_To>::other type;
+#endif
+};
+
 // allocator_traits
 
 namespace __has_pointer_type_imp