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.
........

Merged revisions 413102 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@413103 65c4cc65-6c06-0410-ace0-fbb531ad65f3