Arm64 Build

[Meimax]

fixes part of #260

[Shnyte]

@Meimax
I tried your Sconstruct version and it helped greatly, at least for the part related to the arm64 architecture.
I believe there are a few lines of the original Sconstruct that are missing at the end, among which tool_path definitions.
I'm not sure if you discarded those on purpose, but in my case, I had to add them back.
A bit of tinkering is needed, but it is working nonetheless: I finally have my .so ready.
Thanks for your work!