Make CMakeLists.txt match simtkcommon's better.
Make CMakeLists.txt match simtkcommon's better.

Gjacquenot/simbody,robojukie/simbody,elkingtonmcb/simbody,chrisdembia/simbody,chrisdembia/simbody,scamille/simbody,elen4/simbody,robojukie/simbody,Gjacquenot/simbody,simbody/simbody,chrisdembia/simbody,robojukie/simbody,simbody/simbody,Gjacquenot/simbody,elen4/simbody,scamille/simbody,elkingtonmcb/simbody,elkingtonmcb/simbody,scamille/simbody