[Bug c++/93257] consteval functions returning 'void' are rejected when called

[alisdairm at me dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93257

--- Comment #2 from Alisdair Meredith <alisdairm at me dot com> ---
I am trying to use these extensively as ways to collect related static
assertions in my test suite for <concepts> and <type_traits>.  By using
consteval rather then constexpr, I get notified if any code is unexpectedly
deferred to runtime, and can fix my own bugs.