Make some new algorithms work in parallel mode

	* include/experimental/algorithm (experimental::sample): Qualify call
	to __sample correctly.
	* include/parallel/algo.h (sample, for_each_n): Add using-declarations
	for algorithms that don't have parallel implementations.

From-SVN: r276432

libstdc++-v3/ChangeLog

 2019-10-01  Jonathan Wakely  <jwakely@redhat.com>
 
+	* include/experimental/algorithm (experimental::sample): Qualify call
+	to __sample correctly.
+	* include/parallel/algo.h (sample, for_each_n): Add using-declarations
+	for algorithms that don't have parallel implementations.
+
 	* include/parallel/algobase.h (equal, lexicographical_compare): Add
 	_GLIBCXX20_CONSTEXPR and dispatch to sequential algorithm when being
 	constant evaluated.

libstdc++-v3/include/experimental/algorithm

@@ -77,9 +77,9 @@ inline namespace fundamentals_v2
 		    "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<_UniformRandomNumberGenerator>(__g));
+      return _GLIBCXX_STD_A::
+	__sample(__first, __last, __pop_cat{}, __out, __samp_cat{}, __d,
+		 std::forward<_UniformRandomNumberGenerator>(__g));
     }
 
   template<typename _PopulationIterator, typename _SampleIterator,

libstdc++-v3/include/parallel/algo.h

@@ -2189,6 +2189,11 @@ namespace __parallel
       return __min_element_switch(__begin, __end, __comp,
 				  std::__iterator_category(__begin));
     }
+
+#if __cplusplus >= 201703L
+  using _GLIBCXX_STD_A::for_each_n;
+  using _GLIBCXX_STD_A::sample;
+#endif
 } // end namespace
 } // end namespace