x86_64-apple-ios target

[raphaelrobert]

As discussed, I looked up the necessary targets needed for iOS.

I think the two important ones are aarch64-apple-ios and x86_64-apple-ios (simulator).

For completeness, there are also these 32-bit targets (but I'm not sure how relevant they still are in practical terms):

armv7-apple-ios, armv7s-apple-ios, i386-apple-ios (simulator)

[franziskuskiefer]

32-bit has been removed in iOS 11, we won't be supporting that (unless someone contributes it). Let's add two targets.

• aarch64-apple-ios will be similar to Support aarch64-apple-darwin #26 (aarch64-apple-darwin)
• x86_64-apple-ios

[franziskuskiefer]

For the simulator there is another target that might be interesting (for ios simulators on arm-based macOS).

• aarch64-apple-ios-sim

[franziskuskiefer]

When the hacl* build changes in this PR landed we can continue here.

[franziskuskiefer]

Keeping this open for the x86_64-apple-ios target.