[Bug libstdc++/64399] g++ does not diagnose when upcasting owning pointer (e.g. unique_ptr) with non-virtual destructor

[mw_triad at users dot sourceforge.net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64399

--- Comment #2 from Matthew Woehlke <mw_triad at users dot sourceforge.net> ---
(In reply to Jonathan Wakely from comment #1)
> PR 58876

*Almost*, except I am proposing that -Wnon-virtual-dtor should trip even if X
does not otherwise have virtual methods. (Just why you'd be writing such code,
I'm not sure, but...)

Odd that didn't turn up in my search for existing bugs...