Need to verify the instructions in the Documentation folder for building this repo on different distos have no missing steps. [Windows](https://github.com/dotnet/machinelearning/blob/master/Documentation/building/windows-instructions.md) * Has been verified already. [Unix](https://github.com/dotnet/machinelearning/blob/master/Documentation/building/unix-instructions.md): * Linux: clang version 3.9+ is the minimum pre-requisite not 3.5+ * macOS: to be verified. cc: @danmosemsft @eerhardt
