title: generate data for multiple architectures with cl.exe
body: <p>I'm exporting some MatLab code to C and compiling it with Visual Studio 2013 (cl.exe). I could switch to VS2015 if it helps. The vectorization is very important to me. If I use /O2 it generates the SSE2 code in addition to some fallback code in case it is executed on a non-SSE2 CPU. If I change the architecture to parameter to AVX2, will it generate that code and AVX code and SSE2 code and the fallback code? That's what I want -- run as fast as possible on any CPU. Or will it go straight to the fallback code if the CPU does not support AVX2?</p>