Streamline implementation of GetUniqueIntID:
Streamline implementation of GetUniqueIntID:

- if available, always use the GCC intrinsic function
- otherwise fall back on OS provided atomic operations
- TODO: support other platforms (e.g. Intel compiler)

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