[Bug c++/81787] [5/6/7/8 Regression] `#pragma GCC diagnostic warning "-fpermissive"` no longer works since gcc 4.8

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81787

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Accepting invalid C++ changes the language. It's not a diagnostic option, it's
closer to -std in meaning.