[Bug c++/88323] implement C++20 language features.

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88323
Bug 88323 depends on bug 91353, which changed state.

Bug 91353 Summary: Implement P1331R2: Permitting trivial default initialization 
in constexpr contexts
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91353

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED