commit ec12ddd1e7f7d6b48a593df865e7846039e7d62e
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Jan 6 11:11:52 2022

    libstdc++: Adjust friend declarations to work with Clang
    
    I think this code is valid but it fails with Clang, possibly due to
    https://llvm.org/PR38882
    
    Qualifying the names makes it work for all compilers.
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/regex.h (basic_regex, match_results): Qualify
            name in friend declaration, to work around Clang bug.

diff --git a/libstdc++-v3/include/bits/regex.h b/libstdc++-v3/include/bits/regex.h
index 7480b0a5f97..46c168010bf 100644
--- a/libstdc++-v3/include/bits/regex.h
+++ b/libstdc++-v3/include/bits/regex.h
@@ -796,7 +796,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 	__detail::__regex_algo_impl(_Bp, _Bp, match_results<_Bp, _Ap>&,
 				    const basic_regex<_Cp, _Rp>&,
 				    regex_constants::match_flag_type,
-				    _RegexExecutorPolicy, bool);
+				    __detail::_RegexExecutorPolicy, bool);
 
       template<typename, typename, typename, bool>
 	friend class __detail::_Executor;
@@ -2067,7 +2067,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 	__detail::__regex_algo_impl(_Bp, _Bp, match_results<_Bp, _Ap>&,
 				    const basic_regex<_Cp, _Rp>&,
 				    regex_constants::match_flag_type,
-				    _RegexExecutorPolicy, bool);
+				    __detail::_RegexExecutorPolicy, bool);
 
       // Reset contents to __size unmatched sub_match objects
       // (plus additional objects for prefix, suffix and unmatched sub).