MB-10785: Fix "make clean" when part of larger build

Change-Id: Iaece4266e06d3bc224658a6a53cd27bd80eea390
Reviewed-on: http://review.couchbase.org/35436
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Chris Hillery <ceej@couchbase.com>