[Bug c++/65312] Implicitly-declared default constructor must be defined as deleted

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65312

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I believe this is a GCC extension, G++ implements the proposed resolution of
http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#253 and since all
sub-objects of List are correctly initialized, no initializer is required for
the member of that type.