zpool wait brought in sem_init() and family, which is a primitive set
not previously used in Open ZFS. It also happens to be deprecated
on macOS. Replace with phtread API calls.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: John Gallagher <john.gallagher@delphix.com>
Signed-off-by: Jorgen Lundman <lundman@lundman.net>
Closes#10468