libstdc++: Add comment to __cpp_lib_bitset preprocessor condition

libstdc++-v3/ChangeLog:

	* include/std/bitset: Add comment to feature test macro test.

diff --git a/libstdc++-v3/include/std/bitset b/libstdc++-v3/include/std/bitset
index 6fd32657863f4e0db02954018b712ac9931f85c6..ece359369094585b4e38990af1ae6b5c13e8aff4 100644 (file)
--- 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.