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

[redi at gcc dot gnu.org via Gcc-bugs]

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

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I think it was that change for Bug 99612, which means that (some?) locations
for (some?) warnings are no longer considered to be in system headers, so no
longer suppressed by -isystem and the system_header pragma.