This should fix running the libc++ unit tests.
They failed due to the changes introduced in 67c88e.
// <numeric>
// UNSUPPORTED: clang-8
+// UNSUPPORTED: gcc-9
// Became constexpr in C++20
// template <InputIterator Iter, MoveConstructible T>
// <numeric>
// UNSUPPORTED: clang-8
+// UNSUPPORTED: gcc-9
// Became constexpr in C++20
// template <InputIterator Iter, MoveConstructible T,
// <numeric>
// UNSUPPORTED: clang-8
+// UNSUPPORTED: gcc-9
// Became constexpr in C++20
// template <InputIterator InIter,
// <numeric>
// UNSUPPORTED: clang-8
+// UNSUPPORTED: gcc-9
// Became constexpr in C++20
// template <InputIterator InIter,
// <numeric>
// UNSUPPORTED: c++03, c++11, c++14
// UNSUPPORTED: clang-8
+// UNSUPPORTED: gcc-9
// Became constexpr in C++20
// template<class InputIterator, class OutputIterator, class T>
// <numeric>
// UNSUPPORTED: c++03, c++11, c++14
// UNSUPPORTED: clang-8
+// UNSUPPORTED: gcc-9
// Became constexpr in C++20
// template<class InputIterator, class OutputIterator, class T, class BinaryOperation>
// <numeric>
// UNSUPPORTED: c++03, c++11, c++14
// UNSUPPORTED: clang-8
+// UNSUPPORTED: gcc-9
// Became constexpr in C++20
// template<class InputIterator, class OutputIterator, class T>
// <numeric>
// UNSUPPORTED: c++03, c++11, c++14
// UNSUPPORTED: clang-8
+// UNSUPPORTED: gcc-9
// Became constexpr in C++20
// template<class InputIterator, class OutputIterator, class T, class BinaryOperation>
// <numeric>
// UNSUPPORTED: c++03, c++11, c++14
// UNSUPPORTED: clang-8
+// UNSUPPORTED: gcc-9
// Became constexpr in C++20
// template<class InputIterator, class OutputIterator, class T, class BinaryOperation>
// <numeric>
// UNSUPPORTED: clang-8
+// UNSUPPORTED: gcc-9
// Became constexpr in C++20
// template <InputIterator Iter1, InputIterator Iter2, MoveConstructible T>
// <numeric>
// UNSUPPORTED: clang-8
+// UNSUPPORTED: gcc-9
// Became constexpr in C++20
// template <InputIterator Iter1, InputIterator Iter2, MoveConstructible T,
// <numeric>
// UNSUPPORTED: clang-8
+// UNSUPPORTED: gcc-9
// Became constexpr in C++20
// template <class ForwardIterator, class T>
// <numeric>
// UNSUPPORTED: clang-8
+// UNSUPPORTED: gcc-9
// Became constexpr in C++20
// template <InputIterator InIter, OutputIterator<auto, const InIter::value_type&> OutIter>
// <numeric>
// UNSUPPORTED: clang-8
+// UNSUPPORTED: gcc-9
// Became constexpr in C++20
// template<InputIterator InIter,
// <numeric>
// UNSUPPORTED: c++03, c++11, c++14
// UNSUPPORTED: clang-8
+// UNSUPPORTED: gcc-9
// Became constexpr in C++20
// template<class InputIterator>
// <numeric>
// UNSUPPORTED: c++03, c++11, c++14
// UNSUPPORTED: clang-8
+// UNSUPPORTED: gcc-9
// Became constexpr in C++20
// template<class InputIterator, class T>
// <numeric>
// UNSUPPORTED: c++03, c++11, c++14
// UNSUPPORTED: clang-8
+// UNSUPPORTED: gcc-9
// Became constexpr in C++20
// template<class InputIterator, class T, class BinaryOperation>
// <numeric>
// UNSUPPORTED: c++03, c++11, c++14
// UNSUPPORTED: clang-8
+// UNSUPPORTED: gcc-9
// Became constexpr in C++20
// template<class InputIterator, class OutputIterator, class T,
// <numeric>
// UNSUPPORTED: c++03, c++11, c++14
// UNSUPPORTED: clang-8
+// UNSUPPORTED: gcc-9
// Became constexpr in C++20
// template<class InputIterator, class OutputIterator, class T,
// <numeric>
// UNSUPPORTED: c++03, c++11, c++14
// UNSUPPORTED: clang-8
+// UNSUPPORTED: gcc-9
// Became constexpr in C++20
// template<class InputIterator, class OutputIterator, class T,
// <numeric>
// UNSUPPORTED: c++03, c++11, c++14
// UNSUPPORTED: clang-8
+// UNSUPPORTED: gcc-9
// Became constexpr in C++20
// template <class InputIterator1, class T,
// <numeric>
// UNSUPPORTED: c++03, c++11, c++14
// UNSUPPORTED: clang-8
+// UNSUPPORTED: gcc-9
// Became constexpr in C++20
// template <class InputIterator1, class InputIterator2, class T>
// <numeric>
// UNSUPPORTED: c++03, c++11, c++14
// UNSUPPORTED: clang-8
+// UNSUPPORTED: gcc-9
// Became constexpr in C++20
// template <class InputIterator1, class InputIterator2, class T,