[Bug tree-optimization/119388] [12/13/14/15 Regression] -isystem does not disable warnings coming from system headers

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119388

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Giuseppe D'Angelo from comment #5)
> Are they all *supposed* to be emitted even from system headers?

Yes because they might not be false positives. Even in the bug report you filed
here is a true positive.

because things get inlined and such we want to warn about some undefined code.
If you have an example of a false positive instead, we will improve that case
instead of working around it via hiding it via system headers.