[Bug libstdc++/106839] Library traits need to handle array of incomplete type with unknown bound

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106839

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Actually is_pod_v<Inc[]> really should be ill-formed, so r13-25 was wrong to
allow that.

But is_final_v<Inc[]> should be valid, and is rejected by gcc-11 and gcc-12, so
the library needs to handle that.