[Bug libstdc++/92057] variant converting constructor fails for primitives

[pj at patrickjohnston dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92057

--- Comment #5 from pj at patrickjohnston dot org ---
So then why does `std::variant<Double>{600}` work just fine? (Where `Double` is
defined by `struct Double { double x; Double(int){} };`)