Disable building libcvmfs.a on MacOS
Disable building libcvmfs.a on MacOS

alhowaidi/cvmfsNDN,bbockelm/cvmfs,djw8605/cvmfs,btovar/cvmfs,MicBrain/cvmfs,trshaffer/cvmfs,alhowaidi/cvmfsNDN,DrDaveD/cvmfs,Gangbiao/cvmfs,cvmfs/cvmfs,bbockelm/cvmfs,Moliholy/cvmfs,Gangbiao/cvmfs,cvmfs/cvmfs,btovar/cvmfs,DrDaveD/cvmfs,bbockelm/cvmfs,DrDaveD/cvmfs,ruvolof/cvmfs,cvmfs/cvmfs,cvmfs/cvmfs,cvmfs-testing/cvmfs,cvmfs/cvmfs,Moliholy/cvmfs,trshaffer/cvmfs,Gangbiao/cvmfs,ruvolof/cvmfs,cvmfs-testing/cvmfs,cvmfs/cvmfs,reneme/cvmfs,alhowaidi/cvmfsNDN,Moliholy/cvmfs,MicBrain/cvmfs,MicBrain/cvmfs,btovar/cvmfs,trshaffer/cvmfs,djw8605/cvmfs,Gangbiao/cvmfs,ruvolof/cvmfs,alhowaidi/cvmfsNDN,djw8605/cvmfs,Gangbiao/cvmfs,djw8605/cvmfs,DrDaveD/cvmfs,ruvolof/cvmfs,DrDaveD/cvmfs,cvmfs-testing/cvmfs,reneme/cvmfs,reneme/cvmfs,cvmfs-testing/cvmfs,bbockelm/cvmfs,btovar/cvmfs,ruvolof/cvmfs,bbockelm/cvmfs,reneme/cvmfs,MicBrain/cvmfs,cvmfs-testing/cvmfs,trshaffer/cvmfs,alhowaidi/cvmfsNDN,djw8605/cvmfs,DrDaveD/cvmfs,cvmfs/cvmfs,DrDaveD/cvmfs,Moliholy/cvmfs,trshaffer/cvmfs,Moliholy/cvmfs,reneme/cvmfs,btovar/cvmfs,MicBrain/cvmfs