Specify instruction set

[jtilly]

It would be great if we could specify the instruction set when compiling and not necessarily compile for march=native.

[siboehm]

I think an march parameter added to Model.compile() would make sense:

• march=native: use host cpu architecture + all host cpu features.
• march=<something else>: Use the specified architecture + all features available on this architecture (and newer). I'm not quite sure how to lookup the common CPU features for non-native architectures, but I will investigate.

Default would still be march=native.

[siboehm]

Note to self: I seems like the llvmlite pip packages only ship the backends required for the local arch, hence there's no way to set-up lleaves as a proper cross-compiler.