PR libstdc++/89851 Add testcase for std::variant equality

Add a test for the regression introduced with r269422 and fixed with
r270056.

	PR libstdc++/89851
	* testsuite/20_util/variant/89851.cc: New test.

From-SVN: r270249

libstdc++-v3/ChangeLog

+2019-04-10  Jonathan Wakely  <jwakely@redhat.com>
+
+	PR libstdc++/89851
+	* testsuite/20_util/variant/89851.cc: New test.
+
 2019-04-09  Jonathan Wakely  <jwakely@redhat.com>
 
 	* include/std/variant: Adjust whitespace. Add comments.

libstdc++-v3/testsuite/20_util/variant/89851.cc

+// Copyright (C) 2019 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++17" }
+// { dg-do run { target c++17 } }
+
+#include <variant>
+#include <testsuite_hooks.h>
+
+// PR libstdc++/89851
+
+void
+test01()
+{
+  using V = std::variant<int, int>;
+  V v1{std::in_place_index<0>, 0};
+  V v2{std::in_place_index<1>, 0};
+  VERIFY(   v1 != v2  );
+  VERIFY( !(v1 == v2) );
+}
+
+int
+main()
+{
+  test01();
+}