LWG 3062 - Unnecessary decay_t in is_execution_policy_v

    * include/pstl/execution_defs.h (__enable_if_execution_policy):
    Use std::__remove_cvref_t when building with GCC.

From-SVN: r271489

libstdc++-v3/ChangeLog

+2019-05-21  Thomas Rodgers  <trodgers@redhat.com>
+
+	LWG 3062 - Unnecessary decay_t in is_execution_policy_v
+	* include/pstl/execution_defs.h (__enable_if_execution_policy):
+	Use std::__remove_cvref_t when building with GCC.
+
 2019-05-21  Jonathan Wakely  <jwakely@redhat.com>
 
 	PR libstdc++/90252

libstdc++-v3/include/pstl/execution_defs.h

@@ -152,9 +152,15 @@ constexpr bool is_execution_policy_v = __pstl::execution::is_execution_policy<_T
 namespace __internal
 {
 template <class _ExecPolicy, class _Tp>
+#if _GLIBCXX_RELEASE >= 9
+using __enable_if_execution_policy =
+    typename std::enable_if<__pstl::execution::is_execution_policy<std::__remove_cvref_t<_ExecPolicy>>::value,
+                            _Tp>::type;
+#else
 using __enable_if_execution_policy =
     typename std::enable_if<__pstl::execution::is_execution_policy<typename std::decay<_ExecPolicy>::type>::value,
                             _Tp>::type;
+#endif
 } // namespace __internal
 
 } // namespace __pstl