[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 #12 from pj at patrickjohnston dot org ---
Intentions aside, the concrete change given at the bottom of the paper doesn't
seem to reflect the non-narrowing conversion constraint