The comment is obsolete because char_traits.h do not include stl_algobase.h
anymore and stl_algobase.h is included directly from <string> a few lines
below.
libstdc++-v3/ChangeLog:
* include/std/string: Remove obsolete comment about char_traits.h including
stl_algobase.h.
#include <bits/c++config.h>
#include <bits/stringfwd.h>
-#include <bits/char_traits.h> // NB: In turn includes stl_algobase.h
+#include <bits/char_traits.h>
#include <bits/allocator.h>
#include <bits/cpp_type_traits.h>
#include <bits/localefwd.h> // For operators >>, <<, and getline.