[Bug libstdc++/77641] std::variant copy-initialization fails for type with non-trivial constexpr ctor

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77641

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #1)
> std::string_view is a literal type, but is not trivially default
> constructible.

Oops, I meant X is a literal type (my original code uses variant<int,
string_view> but I reduced it to variant<X> for this report).