On systems without /proc/fd symlinks (and shadow_copy2) is broken

In 4.19 symlinks to directories are broken on systems without support for "Safe File Handle Reopen" like AIX and MR !3472 (closed) demonstrates the symlink bug in 4.19.

In master the problem doesn't surface due to changed semantics of the fsp_name of symlink. In master when a client opens a path that contains a symlink, the resulting fsp->fsp_name will be the resolved symlink target while in previous versions we used the client requested path.

Nevertheless, the functions symlink_target_below_conn() has a bug when dealing with dirfsps == conn->cwd_fsp. This fixes it.

This also updates the no-opath CI runner to cover at least one additional OS (AIX), as the current config doesn't match any known OS.