[Bug libstdc++/87020] comparison operator isn't called for stateless allocator without is_always_equal for C++11/14

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87020

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This property of the library is documented:
https://gcc.gnu.org/onlinedocs/libstdc++/manual/bugs.html#manual.bugs.dr2108