These worked in identical fashion to what the default copy
constructors would be, but their mere presence marks the class
as being "non-trivially copyable," which means that memcpy'ing
it is now a -Werror on GCC 8.
We have to be careful when making this change, though: classes
which *are* trivially copyable can be passed inside registers
on x86_64, so changes like these break ABI in a dangerous way.
These classes is private, so it should not be a problem, but
for other classes (e.g. BRect, BPoint) we cannot fix them
properly right now.
7a73df5e2c