libstdc++: Add test accidentally left out of previous commit

	* testsuite/25_algorithms/move_backward/93872.cc: Add test left out of
	previous commit.

libstdc++-v3/ChangeLog

 2020-02-24  Jonathan Wakely  <jwakely@redhat.com>
 
+	* testsuite/25_algorithms/move_backward/93872.cc: Add test left out of
+	previous commit.
+
 	PR libstdc++/93872
 	* include/bits/stl_algobase.h (__memmove): Cast away const before
 	doing move assignment.

libstdc++-v3/testsuite/25_algorithms/move_backward/93872.cc

+// Copyright (C) 2020 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <algorithm>
+
+struct X
+{
+  X() = default;
+
+  X(const X&) = delete;
+  X& operator=(const X&) = delete;
+
+  X(X&&) = default;
+  X& operator=(X&&) = default;
+};
+
+void
+test01()
+{
+  X a[2], b[2];
+  std::move_backward(std::begin(a), std::end(a), std::begin(b));
+}