Add basic macOS arm64 support

[danielledeleo]

This commit adds basic support for building on M1 Macs. For now, libwasmtime.a for macos_aarch64 must be built manually, but that part seems to be working fine.

This workflow works on my M1 MacBook running Monterey:

cd wasmtime
cargo build -p wasmtime-c-api --release

cd ../wasmtime-go
./ci/local.sh ../wasmtime

All the tests pass except for TestTrapFrames and TestTrapModuleName:

=== RUN   TestTrapFrames
    trap_test.go:34: expected 3 frames, got 1
--- FAIL: TestTrapFrames (0.00s)
=== RUN   TestTrapModuleName
    trap_test.go:90: expected 1 frame, got 0
--- FAIL: TestTrapModuleName (0.00s)

[danielledeleo]

It seems that cargo x86_64-apple-darwin can successfully cross compile to aarch64-apple-darwin, so maybe this could be added to the wasmtime Action?

[alexcrichton]

Seems like a good start at least, thanks! I think there's more to do for correctness, yeah, but seems fine to go ahead and land this.