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.