[gcc r16-5281] libstdc++: Add comment to __cpp_lib_bitset preprocessor condition

[Jonathan Wakely]

https://gcc.gnu.org/g:7a5a92a643b883f3ad3c959045f2cd2d1552c1a6

commit r16-5281-g7a5a92a643b883f3ad3c959045f2cd2d1552c1a6
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Nov 14 12:16:05 2025 +0000

    libstdc++: Add comment to __cpp_lib_bitset preprocessor condition
    
    libstdc++-v3/ChangeLog:
    
            * include/std/bitset: Add comment to feature test macro test.

Diff:
---
 libstdc++-v3/include/std/bitset | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/std/bitset b/libstdc++-v3/include/std/bitset
index 6fd32657863f..ece359369094 100644
--- a/libstdc++-v3/include/std/bitset
+++ b/libstdc++-v3/include/std/bitset
@@ -1012,7 +1012,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 	}
 #endif // HOSTED
 
-#ifdef __cpp_lib_bitset
+#ifdef __cpp_lib_bitset // C++ >= 23
       /**
        *  Use a subset of a string view.
        *  @param  __s  A `string_view` of a sequence of `0` and `1` characters.