Export dynamic (weak-linked) symbols correctly.

(closes issue #15193)
 Reported by: eliel
 Patches: 
       20091111__issue15193.diff.txt uploaded by tilghman (license 14)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@231439 65c4cc65-6c06-0410-ace0-fbb531ad65f3