[Bug c++/93968] -Wswitch-default on exhaustive enum class gives warning about missing default case

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93968

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
And see https://gcc.gnu.org/wiki/VerboseDiagnostics#enum_switch