Add deleted std::thread(const thread&&) constructor

	PR libstdc++/78956
	* include/std/thread (thread(const thread&&)): Add deleted
	constructor.
	* testsuite/30_threads/thread/cons/lwg2097.cc: New test.

From-SVN: r244022

libstdc++-v3/ChangeLog

 2017-01-03  Jonathan Wakely  <jwakely@redhat.com>
 
+	PR libstdc++/78956
+	* include/std/thread (thread(const thread&&)): Add deleted
+	constructor.
+	* testsuite/30_threads/thread/cons/lwg2097.cc: New test.
+
 	* doc/xml/manual/spine.xml: Update copyright years.
 	* doc/xml/manual/build_hacking.xml: Fix spelling of libbuilddir.
 	* doc/xml/manual/test.xml: Likewise.

libstdc++-v3/include/std/thread

@@ -108,6 +108,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     // 2097.  packaged_task constructors should be constrained
     thread(thread&) = delete;
     thread(const thread&) = delete;
+    thread(const thread&&) = delete;
 
     thread(thread&& __t) noexcept
     { swap(__t); }

libstdc++-v3/testsuite/30_threads/thread/cons/lwg2097.cc

+// { dg-do compile { target c++11 } }
+// { dg-require-cstdint "" }
+// { dg-require-gthreads "" }
+
+// Copyright (C) 2017 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/>.
+
+#include <thread>
+
+using std::thread;
+using std::is_constructible;
+
+static_assert( !is_constructible<thread, thread&>::value, "" );
+static_assert( !is_constructible<thread, const thread&>::value, "" );
+static_assert( !is_constructible<thread, const thread>::value, "" );