Use configure to determine the prefixes and include directories properly.

This ensures cross-platform compatibility, even among Linux distributions,
which don't always put headers in the same place.

(closes issue #17391)
 Reported by: loloski


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@265747 65c4cc65-6c06-0410-ace0-fbb531ad65f3