[Bug c++/84364] [8 Regression] -Weffc++ warns on "return *this" in template after r253599

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84364

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Insert obligatory "we should fix -Weffc++ or deprecate it" comment.