void create_directory_symlink(const path& to, const path& new_symlink);
void create_directory_symlink(const path& to, const path& new_symlink,
error_code& ec) noexcept;
Effects: Establishes the postcondition, as if by POSIX symlink().
Postconditions: new_symlink resolves to a symbolic link file that contains an unspecified representation of to.
Throws: As specified in [fs.err.report].
[ Note: Some operating systems require symlink creation to identify that the link is to a directory. Portable code should use create_directory_symlink() to create directory symlinks rather than create_symlink() — end note ]
[ Note: Some operating systems do not support symbolic links at all or support them only for regular files. Some file systems (such as the FAT file system) do not support symbolic links regardless of the operating system. — end note ]