add support for macOS arm64, build wheels

[igrr]

This PR adds support for macOS arm64 platforms. Changes are as follows:

1. Handle platform.machine() == arm64 for macOS.

   Upstream wasmtime releases use aarch64-macos as part of the file name. On aarch64 macOS, platform.machine() returns 'arm64' instead. With this change, download-wasmtime.py correctly downloads aarch64-macos binaries and _ffi.py correctly loads them.

2. Build wheels for macOS arm64 in CI. This should close wasmtime arm64 wheel for mac m1 #79.

I ran tests on macOS-arm64 with python 3.8.9 using pytest, and two failures were reported:

FAILED tests/test_trap.py::TestTrap::test_frames - AssertionError: 1 != 3
FAILED tests/test_trap.py::TestTrap::test_frames_no_module - AssertionError: 0 != 1

(The PR is "draft" because of this failure.)

I have also tested a relatively simple project (astyle code formatter compiled to WebAssembly) with this branch, and it worked correctly.

[igrr]

The test failures for other platforms are because of an incompatibility between pytest-flake8 and the recently released flake8 5.x. This should be fixed by tholo/pytest-flake8#88. In the meantime I can pin flake8 to 4.0.1 in setup.py.

[alexcrichton]

This all looks great to me, thanks!

I'm happy to merge as I think the test failures will be fixed in the next release of Wasmtime if you'd like

[igrr]

@alexcrichton Thanks for reviewing! If you don't mind the test failures, sure please go ahead and merge this.

My use case doesn't depend on trap functionality, so I'd be happy to see a new release of wasmtime-py with macOS arm64 wheels even in the current state.

[alexcrichton]

Sounds good!

I think there's a Wasmtime release tomorrow actually, so this should get picked up tomorrow

[mogery]

hi! this PR's changes aren't reflected in the README yet.

[igrr]

@alexcrichton looks like 0.40.0 was released, could you please tag the new version here as well?

[robtaylor]

just to confirm, if I bump VERSION to 0.40.0, download and build the wheel its all working for me on the M2 macbook pro

[alexcrichton]

I'm doing the version bump in #93