[Bug libstdc++/80451] [6/7 Regression] return implicit type conversion to std::experimental::optional does not compile

[krisk0.2017.02.27 at protonmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80451

--- Comment #6 from Денис Крыськов <krisk0.2017.02.27 at protonmail dot com> ---
Seems like a serious bug in compiler.

Jonathan, thanks for quick investigation.