Start using @rpath for MacOSX correctly
Start using @rpath for MacOSX correctly

Introduced in CMake 3 there is a new policy for dealing with
rpath.

Change-Id: I2ddd1c79ce81a7f19d4b49d87fb855b52f1af545
Reviewed-on: http://review.couchbase.org/43396
Reviewed-by: Dave Rigby <a09264da4832c7ff1d3bf1608a19f4b870f93750@couchbase.com>
Tested-by: Trond Norbye <60edd2ef23891a753f231b0c6f161dc634079a93@gmail.com>

vmx/platform,vmx/platform