[Bug libstdc++/79156] incorrect c++ usage in gcc7 void function returns a value

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79156

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to mib.bugzilla from comment #0)
> Changing "friend void" to "friend auto" would be a simple fix.

That wouldn't compile in C++11 mode. I think shouldn't return anything.