[Bug c++/59480] Missing error diagnostic: friend declaration specifying a default argument must be a definition

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59480

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
And the next slide shows a "missing warning", that actually GCC has warned
about since 4.8

And the next slide is a gnu89-inline issue, which would also show up with GCC 5
due to the -std=c11 default.

etc. etc.