[Bug libstdc++/103013] Underconstrained constructor span(_Range&&)

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103013

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
According to the standard, span<Incomplete> is undefined behaviour, see the
last bullet of [res.on.functions].