https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116162
--- Comment #7 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
I have a patch implementing the clang++ behavior, that is, warning by default
in C++20:
116162.C:3:4: warning: explicitly defaulted move constructor is implicitly
deleted [-Wdefaulted-function-deleted]
3 | C(const C&&) = default; // EDG: ok, gcc: No, Clang: No
| ^
116162.C:3:4: note: function is implicitly deleted because its declared type
does not match the type of an implicit move constructor
