void copy_symlink(const path& existing_symlink, const path& new_symlink);
void copy_symlink(const path& existing_symlink, const path& new_symlink,
error_code& ec) noexcept;
Effects: Equivalent to
function(read_symlink(existing_symlink), new_symlink) or
function(read_symlink(existing_symlink, ec), new_symlink, ec), respectively,
where in each case function is create_symlink or
create_directory_symlink as appropriate.
Throws: As specified in [fs.err.report].