[Bug libstdc++/69478] [4.9/5/6 Regression] std::copy/std::move broken with trivial move-only types

[rs2740 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69478

--- Comment #1 from TC <rs2740 at gmail dot com> ---
It seems that the static_assert should check _IsMove and use either
is_copy_assignable<_Tp> or is_move_assignable<_Tp> depending on its value.