[gcc r16-7363] libstdc++: Update guards on __heterogeneous_hash_key and __heterogeneous_tree_key

[Tomasz Kaminski]

https://gcc.gnu.org/g:9b85fcc00ebe850f2ee2c19a0208534544b088a8

commit r16-7363-g9b85fcc00ebe850f2ee2c19a0208534544b088a8
Author: Tomasz Kamiński <tkaminsk@redhat.com>
Date:   Fri Feb 6 12:03:37 2026 +0100

    libstdc++: Update guards on __heterogeneous_hash_key and __heterogeneous_tree_key
    
    The r16-7359-gae04c1afd1526a changed __heterogeneous_key to be
    defined if __glibcxx_associative_heterogeneous_erasure, but missed
    guards on derived __heterogeneous_hash_key and __heterogeneous_tree_key
    concept.
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/hashtable.h (std::__heterogeneous_hash_key)
            [__glibcxx_associative_heterogeneous_erasure]: Changed guard.
            * include/bits/stl_tree.h (std::__heterogeneous_tree_key)
            [__glibcxx_associative_heterogeneous_erasure]: Likewise.
            * include/bits/stl_function.h: Add comment with C++ version
            for __glibcxx_associative_heterogeneous_erasure guard.

Diff:
---
 libstdc++-v3/include/bits/hashtable.h    | 2 +-
 libstdc++-v3/include/bits/stl_function.h | 2 +-
 libstdc++-v3/include/bits/stl_tree.h     | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/libstdc++-v3/include/bits/hashtable.h b/libstdc++-v3/include/bits/hashtable.h
index f7b8905d8ab9..48695c013f38 100644
--- a/libstdc++-v3/include/bits/hashtable.h
+++ b/libstdc++-v3/include/bits/hashtable.h
@@ -3012,7 +3012,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       = __enable_if_t<!__or_<is_integral<_Hash>, __is_allocator<_Hash>>::value>;
 #endif
 
-#ifdef __cpp_concepts
+#ifdef __glibcxx_associative_heterogeneous_erasure // C++ >= 23
 template <typename _Kt, typename _Container>
   concept __heterogeneous_hash_key =
     __transparent_comparator<typename _Container::hasher> &&
diff --git a/libstdc++-v3/include/bits/stl_function.h b/libstdc++-v3/include/bits/stl_function.h
index 1312564216bd..95c24d44b9ef 100644
--- a/libstdc++-v3/include/bits/stl_function.h
+++ b/libstdc++-v3/include/bits/stl_function.h
@@ -1525,7 +1525,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #endif
 #endif
 
-#ifdef __glibcxx_associative_heterogeneous_erasure
+#ifdef __glibcxx_associative_heterogeneous_erasure // C++ >= 23
 template <typename _Kt, typename _Container>
   concept __not_container_iterator =
     (!is_convertible_v<_Kt&&, typename _Container::iterator> &&
diff --git a/libstdc++-v3/include/bits/stl_tree.h b/libstdc++-v3/include/bits/stl_tree.h
index 7a733241ec5b..5d361b55028f 100644
--- a/libstdc++-v3/include/bits/stl_tree.h
+++ b/libstdc++-v3/include/bits/stl_tree.h
@@ -3315,7 +3315,7 @@ namespace __rb_tree
     };
 #endif // C++17
 
-#ifdef __cpp_concepts
+#ifdef __glibcxx_associative_heterogeneous_erasure // C++ >= 23
 template <typename _Kt, typename _Container>
   concept __heterogeneous_tree_key =
     __transparent_comparator<typename _Container::key_compare> &&