[Bug c++/61339] add mismatch between struct and class to non-bugs

[manu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61339

--- Comment #3 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
Meanwhile, I added a FAQ to the wiki:
https://gcc.gnu.org/wiki/FAQ#Wmismatched-tags

Feel free to improve it !