[Bug c++/115744] [C++26] P2747R2 - constexpr placement new

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115744

--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #1)
> Untested WIP patch.

In the conversion lval change, I'd think we want vc_discard for conversion to
void, and to pass through whatever lval for VIEW_CONVERT_EXPR.