Improve the operative system detection in preprocessor code
Improve the operative system detection in preprocessor code

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