PR libstdc++/81221 fix namespace qualification for parallel mode

	PR libstdc++/81221
	* include/bits/stl_algo.h (sample): Qualify with _GLIBCXX_STD_A not
	std.
	* testsuite/25_algorithms/sample/81221.cc: New.

From-SVN: r249692

libstdc++-v3/ChangeLog

+2017-06-27  Jonathan Wakely  <jwakely@redhat.com>
+
+	PR libstdc++/81221
+	* include/bits/stl_algo.h (sample): Qualify with _GLIBCXX_STD_A not
+	std.
+	* testsuite/25_algorithms/sample/81221.cc: New.
+
 2017-06-22  Jonathan Wakely  <jwakely@redhat.com>
 
 	PR libstdc++/81173

libstdc++-v3/include/bits/stl_algo.h

@@ -5831,8 +5831,9 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
 		    "sample size must be an integer type");
 
       typename iterator_traits<_PopulationIterator>::difference_type __d = __n;
-      return std::__sample(__first, __last, __pop_cat{}, __out, __samp_cat{},
-			   __d, std::forward<_UniformRandomBitGenerator>(__g));
+      return _GLIBCXX_STD_A::
+	__sample(__first, __last, __pop_cat{}, __out, __samp_cat{}, __d,
+		 std::forward<_UniformRandomBitGenerator>(__g));
     }
 #endif // C++17
 #endif // C++14

libstdc++-v3/testsuite/25_algorithms/sample/81221.cc

+// 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/>.
+
+// { dg-options "-std=gnu++17" }
+// { dg-do compile { target c++1z } }
+
+#undef _GLIBCXX_PARALLEL
+#define _GLIBCXX_PARALLEL 1
+#include <algorithm>