Circumventing cblas_sgemv segfault in Accelerate

http://article.gmane.org/gmane.comp.python.scientific.devel/19141
https://github.com/numpy/numpy/issues/4007

the compiler warning you are silencing here is not wrong, you are reading into the pointer to tmp, you'd just put tmp here.

it would be simpler to do: 

    system("sysctl -n machdep.cpu.features | grep -q AVX") != 0