Qualify calls to __never_valueless in <variant>

	* include/std/variant (_Variant_storage, _Extra_visit_slot_needed):
	Qualify calls to __never_valueless.

From-SVN: r272508

libstdc++-v3/ChangeLog

 2019-06-20  Jonathan Wakely  <jwakely@redhat.com>
 
+	* include/std/variant (_Variant_storage, _Extra_visit_slot_needed):
+	Qualify calls to __never_valueless.
+
 	* doc/xml/manual/status_cxx2017.xml: Fix outdated reference to
 	C++17 working draft.
 

libstdc++-v3/include/std/variant

@@ -422,7 +422,7 @@ namespace __variant
       constexpr bool
       _M_valid() const noexcept
       {
-	if constexpr (__never_valueless<_Types...>())
+	if constexpr (__variant::__never_valueless<_Types...>())
 	  return true;
 	return this->_M_index != __index_type(variant_npos);
       }
@@ -456,7 +456,7 @@ namespace __variant
       constexpr bool
       _M_valid() const noexcept
       {
-	if constexpr (__never_valueless<_Types...>())
+	if constexpr (__variant::__never_valueless<_Types...>())
 	  return true;
 	return this->_M_index != __index_type(variant_npos);
       }
@@ -799,7 +799,7 @@ namespace __variant
 
       template <typename... _Types>
 	struct _Variant_never_valueless<variant<_Types...>>
-	: bool_constant<__never_valueless<_Types...>()> {};
+	: bool_constant<__variant::__never_valueless<_Types...>()> {};
 
       static constexpr bool value =
 	(is_same_v<_Maybe_variant_cookie, __variant_cookie>