Add -DLIBCOUCHBASE_INTERNAL for lcbutils

Change-Id: I71a7a0955ff9c55e0621ccbfbfae0345a228a8fc
Reviewed-on: http://review.couchbase.org/31679
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>