[Bug c++/91353] Implement P1331R2: Permitting trivial default initialization in constexpr contexts

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91353

--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
The quux case: CONSTRUCTOR_NO_CLEARING is cleared here

2154   /* The result of a constexpr function must be completely initialized. 
*/
2155   if (TREE_CODE (result) == CONSTRUCTOR)
2156     clear_no_implicit_zero (result);

but we can no longer assume that a constexpr constructor has initialized all
the members.