Add apple tvos support

[lcruz99]

This PR allows using tokio lib to target tier 3 *-apple builds:

• Apple tvOS on aarch64
• Apple tvOS Simulator on x86_64

[Darksonn]

Thanks. Would you be able to add a cargo check for this target to CI?

[Darksonn]

We're not going to add a tier 3 target to this list.

[lcruz99]

Rereading it I realize now I shouldn't have touched that, sorry about that.

Thanks. Would you be able to add a cargo check for this target to CI?

Sure, I think so, will add.

[lcruz99]

You can check my last commit where I add the CI job, however this target requires "appropriate versions of Xcode and the SDKs for tvOS (AppleTVOS.sdk) and/or the tvOS Simulator (AppleTVSimulator.sdk) to build a toolchain and target these platforms." As the runner is a x86_64 machine, it cannot build for this target.

[Darksonn]

If we can't add CI, then that's okay. Have you tested that the code works on a real setup?

[lcruz99]

Yes, so far so good! :)

[Darksonn]

Thanks.