[Bug testsuite/114384] Use of `target c++98/c++11/c++20` etc. is not documented

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114384

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Oh and how it interacts with -std=gnu++17 vs -std=c++17 (etc.).