https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92662
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I'm pretty sure GCC 9 is correct. It started to be rejected with r269602:
PR c++/86521 - wrong overload resolution with ref-qualifiers.
Here we were wrongly treating binding a const lvalue ref to an xvalue as
direct binding, which is wrong under [dcl.init.ref] and [over.match.ref].
* call.c (build_user_type_conversion_1): Don't use a conversion to
a
reference of the wrong rvalueness for direct binding.
