[Bug c/70753] missing diagnostic in C11 mode: sizeof, _Alignof of function type

[fw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70753

--- Comment #2 from Florian Weimer <fw at gcc dot gnu.org> ---
(In reply to Marek Polacek from comment #1)
> Why would it have to be error?  If you want errors instead of warnings, use
> -pedantic-errors.

I did not know about -pedantic-errors.  It is extremely surprising that
-std=c11 does not enable all diagnostics required by C11.