[gcc r13-8032] libstdc++: Fix 29_atomics/headers/atomic/types_std_c++2a_neg.cc for C++23

[Jonathan Wakely]

https://gcc.gnu.org/g:4b49dfe2773e064362b13a45c29278094c6a6bb4

commit r13-8032-g4b49dfe2773e064362b13a45c29278094c6a6bb4
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Sep 15 21:37:46 2023 +0100

    libstdc++: Fix 29_atomics/headers/atomic/types_std_c++2a_neg.cc for C++23
    
    This test fails when run as C++23 because the <bits/stdc++.h> PCH
    includes <stdatomic.h> which declares ::memory_order, invalidating the
    test's assumptions. Disable PCH so that the test verifies that <atomic>
    doesn't declare ::memory_order, as originally intended.
    
    Also fix the using-declaration which would be invalid even if the type
    was declared in the global namespace, and adjust the expected error.
    
    libstdc++-v3/ChangeLog:
    
            * testsuite/29_atomics/headers/atomic/types_std_c++2a_neg.cc:
            Fix test to work for C++23 and C++26 too.
    
    (cherry picked from commit 038c0afa893f8cb2277ff44be3e2c09cfab4bc0c)

Diff:
---
 .../testsuite/29_atomics/headers/atomic/types_std_c++2a_neg.cc     | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/testsuite/29_atomics/headers/atomic/types_std_c++2a_neg.cc b/libstdc++-v3/testsuite/29_atomics/headers/atomic/types_std_c++2a_neg.cc
index 8eba8bfd779..65199ce15e5 100644
--- a/libstdc++-v3/testsuite/29_atomics/headers/atomic/types_std_c++2a_neg.cc
+++ b/libstdc++-v3/testsuite/29_atomics/headers/atomic/types_std_c++2a_neg.cc
@@ -1,5 +1,8 @@
 // { dg-options "-std=gnu++2a" }
-// { dg-do compile { target c++2a } }
+// { dg-do compile { target c++20 } }
+// Disable PCH because <bits/stdc++.h> includes <stdatomic.h> which declares
+// memory_order in the global namespace.
+// { dg-add-options no_pch }
 
 // Copyright (C) 2019-2023 Free Software Foundation, Inc.
 //
@@ -23,7 +26,7 @@
 void test01()
 {
   // Not global scoped, only namespace std.
-  using memory_order; // { dg-error "expected nested-name-specifier" }
+  using ::memory_order; // { dg-error "has not been declared" }
   constexpr auto relaxed = memory_order::relaxed; // { dg-error "has not been declared" }
   constexpr auto consume = memory_order::consume; // { dg-error "has not been declared" }
   constexpr auto acquire = memory_order::acquire; // { dg-error "has not been declared" }