Build and publish Theseus documentation for aarch64

[NathanRoyer]

I sometimes run into problems adding such attributes to my code:

#[cfg(any(target_arch = "aarch64", doc))]

because when the documentation gets built, references to aarch64-only symbols are invalid/not found.

The first solution to this would be to declare an x86-equivalent for every such symbol. However sometimes this is bad, for instance in arm_boards it would mean declaring a valid board_config for x86_64 even though this should only be used in aarch64-specific code and definitions.

[hecatia-elegua]

https://doc.rust-lang.org/cargo/commands/cargo-doc.html#compilation-options --target -> This flag may be specified multiple times. I have not tried it, but it might do something.

https://doc.rust-lang.org/rustdoc/advanced-features.html#interactions-between-platform-specific-docs / https://github.com/rust-lang/rust/issues/1998 sounds like it's probably not as easy as I thought