Build system modifications to ensure that Asterisk properly builds on Mac OS X 10.6.

(closes issue #16997)
 Reported by: jquinn
 Patches: 
       20100309__issue16997__2.diff.txt uploaded by tilghman (license 14)
 Tested by: tilghman, russell


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@251475 65c4cc65-6c06-0410-ace0-fbb531ad65f3