Fix CMake 3.0 warning on OSX.
Fix CMake 3.0 warning on OSX.

mp3guy/Pangolin,visigoth/Pangolin,renzodenardi/Pangolin,tschmidt23/Pangolin,wxdzju/Pangolin,stevenlovegrove/Pangolin,pinglin/Pangolin,arpg/Pangolin,pinglin/Pangolin,mp3guy/Pangolin,randi120/Pangolin,tschmidt23/Pangolin,visigoth/Pangolin,stevenlovegrove/Pangolin,stevenlovegrove/Pangolin,arpg/Pangolin,renzodenardi/Pangolin,tschmidt23/Pangolin,randi120/Pangolin,mp3guy/Pangolin,wxdzju/Pangolin