Force symlink creation for zpool.d compat links

gmake install fails when zpool.d compat links already exist.

Force the symlinks to be recreated if already present.

Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ryan Moeller <ryan@iXsystems.com>
Closes #11633