Add "destroy" implementation for spinlock.

The original commit for spinlock was missing "destroy" implementations.
Most of them are no-ops but phtread_spin and pthread_mutex do need their
locks destroyed.



git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/12@413102 f38db490-d61c-443f-a65b-d21fe96a405b