cmake: use FindThreads for threading library flags
cmake: use FindThreads for threading library flags

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