[Bug libstdc++/69259] std::experimental::filesystem::copy does not create symlinks for directories

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69259

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(We are missing tests for filesystem::copy() though, I accidentally duplicated
the tests for fs::absolute())