[gcc r9-9641] libstdc++: Fix test failure in C++20 mode

[Jonathan Wakely]

https://gcc.gnu.org/g:727681335798fa8c4e53148bb24a965640d1e2b1

commit r9-9641-g727681335798fa8c4e53148bb24a965640d1e2b1
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Jul 22 22:26:30 2021 +0100

    libstdc++: Fix test failure in C++20 mode
    
    Because the container types are ambiguous in this test, the declarations
    of the C++20 uniform container erasure function template produce
    additional errors. They can be ignored.
    
    libstdc++-v3/ChangeLog:
    
            * testsuite/ext/profile/mutex_extensions_neg.cc: Prune
            additional errors in C++20 mode.

Diff:
---
 libstdc++-v3/testsuite/ext/profile/mutex_extensions_neg.cc | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/libstdc++-v3/testsuite/ext/profile/mutex_extensions_neg.cc b/libstdc++-v3/testsuite/ext/profile/mutex_extensions_neg.cc
index cd2a48845aa..f34c4fd107e 100644
--- a/libstdc++-v3/testsuite/ext/profile/mutex_extensions_neg.cc
+++ b/libstdc++-v3/testsuite/ext/profile/mutex_extensions_neg.cc
@@ -31,3 +31,6 @@
 // { dg-prune-output "tuple:993" }
 // PMR alias templates cause ambiguities between debug and profile containers:
 // { dg-prune-output "is ambiguous" }
+// C++20 uniform container erasure causes more errors
+// { dg-prune-output "expected nested-name-specifier before" }
+// { dg-prune-output "expected initializer before" }