[Bug c++/109323] No error when neither of return_value or return_void is defined

[arsen at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109323

--- Comment #8 from Arsen Arsenović <arsen at gcc dot gnu.org> ---
iota did come to mind while I was typing that, but my thinking is that it is
far more likely to be unintended, hence my thinking