Add support for aarch64-apple-darwin

[repi]

Did a quick test build for it and seems the main issue is or rpmalloc crate which is lacking support (EmbarkStudios/rpmalloc-rs#11). We could for now disable the custom global allocator for now for this target

[badboy]

Just ran into this. Would you accept a PR that disables that dependency on aarch64-apple-darwin? I can prepare one tomorrow.

[repi]

We probably should just switch to the mimalloc crate which we already use on on all targets (including aarch64-apple-darwin) in other projects.

A PR with that would be most welcome!

[badboy]

Oh, even easier. I can do that too!

[badboy]

Question though: why does this crate even need a custom allocator? Is it that allocation-heavy that it really benefits much from a non-system one?

[Jake-Shadle]

I think it was primarily to speed up x86_64-unknown-linux-musl since its allocator was pretty terrible wrt parallelization and it's easier to just use the same allocator for all targets (until we hit issues like this).

[repi]

Yes I think that was the original issue, and maybe also that on Windows it was really slow with the system allocator that made an actual impact.