Fix a configure issue with PJSIP transaction group lock detection.

The configure check did not use the provided paths for pjproject
if provided when looking for transaction group lock support.
........

Merged revisions 403160 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@403161 65c4cc65-6c06-0410-ace0-fbb531ad65f3