Comment 8 for bug 2030797

The proposed change will compile very slowly, something like this would be better:

--- a/libstdc++-v3/include/pstl/execution_impl.h
+++ b/libstdc++-v3/include/pstl/execution_impl.h
@@ -19,13 +19,24 @@ namespace __pstl
 {
 namespace __internal
 {
+#if __glibcxx_concepts
+template<typename _Iter>
+ concept __is_random_access_iter
+ = std::is_base_of_v<std::random_access_iterator_tag,
+ std::__iter_category_t<_Iter>>
+ || std::random_access_iterator<_Iter>;

+template <typename... _IteratorTypes>
+ using __are_random_access_iterators
+ = std::bool_constant<(__is_random_access_iter<_IteratorTypes> && ...)>;
+#else
 template <typename _IteratorTag, typename... _IteratorTypes>
 using __are_iterators_of = std::conjunction<
     std::is_base_of<_IteratorTag, typename std::iterator_traits<std::decay_t<_IteratorTypes>>::iterator_category>...>;

 template <typename... _IteratorTypes>
 using __are_random_access_iterators = __are_iterators_of<std::random_access_iterator_tag, _IteratorTypes...>;
+#endif

 struct __serial_backend_tag
 {

This uses the libstdc++ helper __iter_category_t but since we no longer need to sync with upstream, that seems fine.