[build] cmake_prefix_path allows radio build to find libjoynr
[build] cmake_prefix_path allows radio build to find libjoynr

Change-Id: I27cbb4a47e220dcb7cf8c324c37d6999a87c64d3

clive-jevons/joynr,bmwcarit/joynr,bmwcarit/joynr,clive-jevons/joynr,bmwcarit/joynr,bmwcarit/joynr,bmwcarit/joynr,bmwcarit/joynr,bmwcarit/joynr,clive-jevons/joynr,clive-jevons/joynr,clive-jevons/joynr,bmwcarit/joynr,clive-jevons/joynr,bmwcarit/joynr