[Bug preprocessor/85211] -isystem automatically adds extern "C" to includes

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85211

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to blastrock from comment #2)
> And I was hoping for a way to disable it at runtime, recompiling
> gcc seems quite complex...

That's not possible.