removed clang option for linux; it's generally too old for avx2, anyway
removed clang option for linux; it's generally too old for avx2, anyway

favreau/OSPRay,Twinklebear/OSPRay,MengjiaoH/ospray,MengjiaoH/ospray,wilsonCernWq/ospray,ospray/OSPRay,Twinklebear/OSPRay,favreau/OSPRay,ospray/OSPRay,wilsonCernWq/ospray,Twinklebear/OSPRay,favreau/OSPRay,ospray/OSPRay,MengjiaoH/ospray,MengjiaoH/ospray,ospray/OSPRay,wilsonCernWq/ospray,MengjiaoH/ospray,Twinklebear/OSPRay,favreau/OSPRay