[Bug c++/66519] [C++14] ICE when using decltype to detect callable return type during SFINAE

[krzysztof.sinica at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66519

--- Comment #1 from Krzysztof Sinica <krzysztof.sinica at gmail dot com> ---
Created attachment 38796
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=38796&action=edit
Reduced repro.