Revert "Stop CMake warning about @rpath on Mac OS X."
Revert "Stop CMake warning about @rpath on Mac OS X."

This reverts commit c9f00dfb9f5ce306398f18cafa143988a4f61515. Because it breaks
under CMake versions that don't know what CMP0042 is.

chenwenbin928/rabbitmq-c,kilinrax/rabbitmq-c,sakishum/rabbitmq-c,tempbottle/rabbitmq-c,jqk6/rabbitmq-c,alanxz/rabbitmq-c,Haster2004/rabbitmq-c,sakishum/rabbitmq-c,Haster2004/rabbitmq-c,kilinrax/rabbitmq-c,hjzljp/rabbitmq-c,tempbottle/rabbitmq-c,alanxz/rabbitmq-c,jqk6/rabbitmq-c,chenwenbin928/rabbitmq-c,soindy/rabbitmq-c,tempbottle/rabbitmq-c,sakishum/rabbitmq-c,chenwenbin928/rabbitmq-c,kilinrax/rabbitmq-c,Haster2004/rabbitmq-c,tempbottle/rabbitmq-c,hjzljp/rabbitmq-c,alanxz/rabbitmq-c,hjzljp/rabbitmq-c,soindy/rabbitmq-c,soindy/rabbitmq-c,hjzljp/rabbitmq-c,jqk6/rabbitmq-c,jqk6/rabbitmq-c