Use the detected pthread building flags in every place, instead of hardcoding -lpthread.

We nicely detect the right flags on each system for building Asterisk with
pthreads, then ignore it for every other build option that requires us to
build with pthreads.  This caused some items to return a false negative.
Also cleanup some minor naming issues that caused "library library" redundancy
in the output.

(closes issue #17303)
 Reported by: stuarth
 Patches: 
       20100507__issue17303.diff.txt uploaded by tilghman (license 14)
 Tested by: stuarth


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@261913 65c4cc65-6c06-0410-ace0-fbb531ad65f3