Fixing compilations issued on OSX due to pthread_spin functions not being defined. 
Fixing compilations issued on OSX due to pthread_spin functions not being defined. 


dariomangoni/chrono,armanpazouki/chrono,Bryan-Peterson/chrono,Bryan-Peterson/chrono,amelmquist/chrono,amelmquist/chrono,rserban/chrono,PedroTrujilloV/chrono,andrewseidl/chrono,armanpazouki/chrono,tjolsen/chrono,dariomangoni/chrono,hsu/chrono,jcmadsen/chrono,tjolsen/chrono,andrewseidl/chrono,projectchrono/chrono,PedroTrujilloV/chrono,jcmadsen/chrono,tjolsen/chrono,rserban/chrono,tjolsen/chrono,hsu/chrono,armanpazouki/chrono,amelmquist/chrono,tjolsen/chrono,Milad-Rakhsha/chrono,PedroTrujilloV/chrono,hsu/chrono,scpeters/chrono,armanpazouki/chrono,scpeters/chrono,scpeters/chrono,jcmadsen/chrono,jcmadsen/chrono,Bryan-Peterson/chrono,dariomangoni/chrono,scpeters/chrono,armanpazouki/chrono,jcmadsen/chrono,dariomangoni/chrono,armanpazouki/chrono,PedroTrujilloV/chrono,projectchrono/chrono,Milad-Rakhsha/chrono,rserban/chrono,Milad-Rakhsha/chrono,amelmquist/chrono,andrewseidl/chrono,rserban/chrono,andrewseidl/chrono,hsu/chrono,projectchrono/chrono,rserban/chrono,projectchrono/chrono,jcmadsen/chrono,dariomangoni/chrono,rserban/chrono,hsu/chrono,amelmquist/chrono,scpeters/chrono,dariomangoni/chrono,Bryan-Peterson/chrono,amelmquist/chrono,Milad-Rakhsha/chrono,projectchrono/chrono,PedroTrujilloV/chrono,projectchrono/chrono,Bryan-Peterson/chrono,jcmadsen/chrono,Milad-Rakhsha/chrono,rserban/chrono,andrewseidl/chrono,Milad-Rakhsha/chrono