Support for Apple M1 aarch64

[skhamis]

Application-services is currently running into an issue with compiling NSS via rust-android-gradle mozilla/application-services#4665.

I believe it's potentially something to do with rust-android-gradle associating Darwin = x86_64 mozilla/application-services#4665 (comment) which works if the Mac is using a JDK = x86_64 but M1's are now defaulting to downloading arm64 (homebrew) JDKs which causes the builds to break.

We probably need to allow the ability for Darwin to = arm64

[ncalexan]

@skhamis thanks for the report. As we discussed on Slack, I'm not aware of any fundamental blocker to making this work. My expectation is that we need to split darwin into darwin-{x86-64,aarch64}. We do run some tests in CI these days, but I'm not sure that we can target macOS aarch64 machines in Github Actions, nor am I sure that we're running any Robolectric style tests.

Let me know how you get on with a patch. Thanks!

[skhamis]

@ncalexan I think it the PR ended up being pretty straightforward! To keep things straightforward and prevent anyone from breaking too bad. I decided to go with keeping darwin and simply adding darwin-x86-64 and aarch64 as new targets to keep things moving. At some point I can make a PR to remove the darwin target once the dust has settled a bit and seems to be stable.

[ncalexan]

This landed and is, I believe, working well for application-services.