[Bug c++/86733] c++17 and #pragma GCC diagnostic warning "-Wall" resurrect pre-c++11 warnings.

[Emmanuel.Thome at inria dot fr]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86733

--- Comment #4 from Emmanuel Thomé <Emmanuel.Thome at inria dot fr> ---
(In reply to Jonathan Wakely from comment #3)
> (In reply to Emmanuel Thomé from comment #2)
> > (In reply to Jonathan Wakely from comment #1)
> > > Presumably the handling for the pragma just turns the option on without
> > > considering the current cxx_dialect.
> > 
> > It seems to me that it is not consistent with the test case compiling fine
> > with g++ -std=c++11 -c foo.cpp , is it ?
> 
> That's why I confirmed it as a bug.

If #pragma were just "turning the option on without considering the dialect",
then my test case would issue a warning with -std=c++11 too. So there's more
stuff that comes into play, it seems.