Fix gcc compilation error.
Fix gcc compilation error.

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