Make cleaner threads.h compile for the NOTHREADS case
Make cleaner threads.h compile for the NOTHREADS case

bdeluca/oiio,lgritz/oiio,bdeluca/oiio,cwilling/oiio,mcanthony/oiio,micler/oiio,sambler/oiio,YangYangTL/oiio,OpenImageIO/oiio,lgritz/oiio,scott-wilson/oiio,mcanthony/oiio,micler/oiio,cwilling/oiio,YangYangTL/oiio,cwilling/oiio,sambler/oiio,bdeluca/oiio,YangYangTL/oiio,bdeluca/oiio,scott-wilson/oiio,lgritz/oiio,YangYangTL/oiio,scott-wilson/oiio,sambler/oiio,OpenImageIO/oiio,scott-wilson/oiio,OpenImageIO/oiio,cwilling/oiio,lgritz/oiio,sambler/oiio,micler/oiio,OpenImageIO/oiio,mcanthony/oiio,micler/oiio,mcanthony/oiio