Fix how we build pjproject.

Allow parallel builds, better tolerate failures, build faster.

This also stops running dependencies before top-level configure has been run.

(closes issue ASTERISK-20815)

Review: https://reviewboard.asterisk.org/r/2292/
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Merged revisions 380816 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@380817 65c4cc65-6c06-0410-ace0-fbb531ad65f3