[Bug libstdc++/85965] [8/9 Regression] G++ gives cryptic error instead of incomplete type

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85965

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
No problem, it's not the reporter's responsibility to categorise it correctly.