<ext/bitmap_allocator.h> includes <function>, and since C++17 that
includes <unordered_map>. If std::allocator is defined in terms of
__gnu_cxx::bitmap_allocator then you get a circular reference and
bootstrap fails when compiling src/c++17/*.cc.
libstdc++-v3/ChangeLog:
PR libstdc++/103381
* include/ext/bitmap_allocator.h: Include <bits/stl_function.h>
instead of <functional>.
#include <utility> // For std::pair.
#include <bits/functexcept.h> // For __throw_bad_alloc().
-#include <functional> // For greater_equal, and less_equal.
+#include <bits/stl_function.h> // For greater_equal, and less_equal.
#include <new> // For operator new.
#include <debug/debug.h> // _GLIBCXX_DEBUG_ASSERT
#include <ext/concurrence.h>