fix compile error on  macOS
fix compile error on  macOS

Gangbiao/cvmfs,DrDaveD/cvmfs,cvmfs/cvmfs,cvmfs/cvmfs,Gangbiao/cvmfs,cvmfs/cvmfs,Gangbiao/cvmfs,Gangbiao/cvmfs,cvmfs/cvmfs,cvmfs/cvmfs,DrDaveD/cvmfs,cvmfs/cvmfs,Gangbiao/cvmfs,DrDaveD/cvmfs,DrDaveD/cvmfs,cvmfs/cvmfs,DrDaveD/cvmfs,DrDaveD/cvmfs,DrDaveD/cvmfs