[libc++] Mark my new <algorithm> test unsupported on clang-8.

Because in C++20 mode, it tests that `copy_n` is constexpr;
so it depends on the compiler supporting `is_constant_evaluated`.

diff --git a/libcxx/test/std/algorithms/robust_against_adl.pass.cpp b/libcxx/test/std/algorithms/robust_against_adl.pass.cpp
index fca6f98..a9ea46a 100644 (file)
--- a/libcxx/test/std/algorithms/robust_against_adl.pass.cpp
+++ b/libcxx/test/std/algorithms/robust_against_adl.pass.cpp
@@ -6,6 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+// UNSUPPORTED: clang-8
 // UNSUPPORTED: c++03
 
 // <algorithm>