Support Aarch64Call relocations for Mach-O

[nathanwhit]

This PR adds support for relocations with RelocationEncoding::Aarch64Call on Mach-O. Before this PR we would error out, as the relocation has a size of 26 which was unhandled, and we weren't setting the appropriate r_type. After this PR we support relocations with RelocationEncoding::Aarch64Call and an arbitrary addend.

This PR also handles a few extra cases of the relocation size (21 and 12) in order to support the usage of Mach-O specific relocations like ARM64_RELOC_PAGE21 and ARM64_RELOC_PAGEOFF12, respectively.

[philipc]

Thanks! Based on a brief look this is good. Where was the panic occurring?

[nathanwhit]

The original panic was at

object/src/write/macho.rs

Line 551 in 13c1392

_ => return Err(Error(format!("unimplemented reloc size {:?}", reloc))),

Once that was fixed, it was hitting this case

object/src/write/macho.rs

Line 599 in 13c1392

return Err(Error(format!("unimplemented relocation {:?}", reloc)));

[philipc]

Ah okay, so not panics, just returning errors (maybe your crate was unwrapping that error).

[nathanwhit]

Ah sorry, of course, don't know how I managed to mix that up. (The panic I was seeing was from cranelift unwrapping that error, here to be precise).

[philipc]

Thanks! I'll merge this after the unrelated archive code has been fixed.

[nathanwhit]

(Rebased so that CI passes now that the formatting issue has been fixed on master)