Fix DEBUG_THREADS build on Darwin.

(closes issue #16828)
 Reported by: oej
 Patches: 
       20100331__issue16828.diff.txt uploaded by tilghman (license 14)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@255796 65c4cc65-6c06-0410-ace0-fbb531ad65f3