Support other architectures

[adam-azarchs]

Currently there are a few things that are hard-coded to linux/amd64. There isn't a good reason for this other than that we haven't had a need for anything else up to now. We should attempt to support all of the architecture/OS pairings that are supported on conda-forge.

Supporting linux/aarch64 should be pretty straightforward. It just means detecting the architecture from the package path rather than hard-coding the assumption of amd64.

Supporting darwin is a little more complex due to a few things that assume dynamic libraries and python extension modules use a .so extension. There's also one place that assumes they are in ELF format, but having that bit working might not even be required under OSX.

Windows is more complex due to executables having the .exe file extension appended; we might not ever get to that.