Check python and target arcitecture match in build.rs

[davidhewitt]

Fixes #752

[kngwyu]

Thank you!

[oconnor663]

I'm not sure this is accurate when running 32-bit Python on a 64-bit platform. For example see this run: https://github.com/oconnor663/blake3-py/runs/527998905

That's building with 32-bit Python, on a 64-bit Windows host. When I expand the the " Run python tests/python_info.py" step (which runs this script), I see this output:

{
  "libdir": null,
  "platform": "Windows-10-10.0.17763-SP0",
  "architecture": [
    "32bit",
    "WindowsPE"
  ],
  "version": {
    "implementation": "CPython",
    "minor": 5,
    "major": 3
  },
  "ld_version": "3.5",
  "executable": "C:\\hostedtoolcache\\windows\\Python\\3.5.4\\x86\\python.exe",
  "machine": "AMD64",
  "base_prefix": "C:\\hostedtoolcache\\windows\\Python\\3.5.4\\x86",
  "shared": false,
  "maxsize_bits": 31
}

Specifically, machine is AMD64, but architecture and maxsize_bits indicate 32-bit Python. I think that's causing the build to get confused later. I'll start working on a PR, but please let me know if I'm misunderstanding the intended behavior here.

[davidhewitt]

@oconnor663 it is very possible I misunderstood the literature out there on how to detect the Python architecture correctly. Please do open a PR 🙏