Before this change, if writing to a local backend with --metadata and
--links, if the incoming metadata contained mode or ownership
information then rclone would apply the mode/ownership to the
destination of the link not the link itself.
This fixes the problem by using the link safe sycall variants
lchown/fchmodat when --links and --metadata is in use. Note that Linux
does not support setting permissions on symlinks, so rclone emits a
debug message in this case.
This also fixes setting times on symlinks on Windows which wasn't
implemented for atime, mtime and was incorrectly setting the target of
the symlink for btime.
See: https://github.com/rclone/rclone/security/advisories/GHSA-hrxh-9w67-g4cv
Before this change this would give errors like this
failed to set metadata on directory: failed to set birth (creation) time: Access is denied.
This was caused by opening the directory in the wrong mode.
