[Bug libstdc++/103381] [9/10/11 Regression] --enable-libstdcxx-allocator=bitmap doesn't build

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103381

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Every test fails with:

/usr/bin/ld: .../libstdc++-v3/src/.libs/libstdc++.so: undefined reference to
`__gnu_cxx::bitmap_allocator<unsigned int>::_S_last_request'
/usr/bin/ld: .../libstdc++-v3/src/.libs/libstdc++.so: undefined reference to
`__gnu_cxx::bitmap_allocator<std::_Sp_counted_ptr_inplace<std::mutex,
std::allocator<std::mutex>, (__gnu_cxx::_Lock_policy)2> >::_S_mut'
/usr/bin/ld: .../libstdc++-v3/src/.libs/libstdc++.so: undefined reference to
`__gnu_cxx::bitmap_allocator<std::_Sp_counted_ptr_inplace<std::__future_base::_State_baseV2,
std::allocator<std::__future_base::_State_baseV2>, (__gnu_cxx::_Lock_policy)2>
>::_S_mut'
/usr/bin/ld: .../libstdc++-v3/src/.libs/libstdc++.so: undefined reference to
`__gnu_cxx::bitmap_allocator<std::_Sp_counted_ptr_inplace<std::mutex,
std::allocator<std::mutex>, (__gnu_cxx::_Lock_policy)2> >::_S_mem_blocks'
/usr/bin/ld: .../libstdc++-v3/src/.libs/libstdc++.so: undefined reference to
`__gnu_cxx::bitmap_allocator<std::_Sp_counted_ptr_inplace<std::__future_base::_State_baseV2,
std::allocator<std::__future_base::_State_baseV2>, (__gnu_cxx::_Lock_policy)2>
>::_S_last_request'
/usr/bin/ld: .../libstdc++-v3/src/.libs/libstdc++.so: undefined reference to
`__gnu_cxx::bitmap_allocator<unsigned int>::_S_mut'
/usr/bin/ld: .../libstdc++-v3/src/.libs/libstdc++.so: undefined reference to
`__gnu_cxx::bitmap_allocator<unsigned int>::_S_mem_blocks'
/usr/bin/ld: .../libstdc++-v3/src/.libs/libstdc++.so: undefined reference to
`__gnu_cxx::bitmap_allocator<std::_Sp_counted_ptr_inplace<std::mutex,
std::allocator<std::mutex>, (__gnu_cxx::_Lock_policy)2> >::_S_last_request'
/usr/bin/ld: .../libstdc++-v3/src/.libs/libstdc++.so: undefined reference to
`__gnu_cxx::bitmap_allocator<std::_Sp_counted_ptr_inplace<std::__future_base::_State_baseV2,
std::allocator<std::__future_base::_State_baseV2>, (__gnu_cxx::_Lock_policy)2>
>::_S_mem_blocks'

So this configure option seems broken, and nobody seems to have noticed.