[Bug libstdc++/85965] [8 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 #11 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The example reported here is fixed in 9.1.0, if you have a different example
maybe there's a different problem.