https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88095
--- Comment #2 from Tom Honermann <tom at honermann dot net> --- I confirmed that Jeff's patch, applied to gcc 9.1.0, suffices to address both Hana's test case and the code in the "Emulate C++17 u8 literals" section of P1423R2 (http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1423r2.html#emulate) if the declaration of operator <=> is commented out (since gcc doesn't yet support operator <=>).
