arti-client fails to compile on `aarch64-apple-ios-sim` target

Discovered during the Tor VPN hacking sessions in Ireland; @tla was trying to build arti-client for the aarch64-apple-ios-sim target, which failed with:

error[E0425]: cannot find function `getresuid` in crate `libc`
   --> /Users/[redacted]/.cargo/registry/src/github.com-1ecc6299db9ec823/arti-client-0.6.0/src/util.rs:56:31
    |
56  |                 let _ = libc::getresuid(&mut resuid[0], &mut resuid[1], &mut resuid[2]);
    |                               ^^^^^^^^^ help: a function with a similar name exists: `geteuid`
    |
   ::: /Users/[redacted]/.cargo/registry/src/github.com-1ecc6299db9ec823/libc-0.2.132/src/unix/mod.rs:871:5
    |
871 |     pub fn geteuid() -> uid_t;
    |     -------------------------- similarly named function `geteuid` defined here

error[E0425]: cannot find function `getresgid` in crate `libc`
   --> /Users/[redacted]/.cargo/registry/src/github.com-1ecc6299db9ec823/arti-client-0.6.0/src/util.rs:57:31
    |
57  |                 let _ = libc::getresgid(&mut resgid[0], &mut resgid[1], &mut resgid[2]);
    |                               ^^^^^^^^^ help: a function with a similar name exists: `getegid`
    |
   ::: /Users/[redacted]/.cargo/registry/src/github.com-1ecc6299db9ec823/libc-0.2.132/src/unix/mod.rs:870:5
    |
870 |     pub fn getegid() -> gid_t;
    |     -------------------------- similarly named function `getegid` defined here

For more information about this error, try `rustc --explain E0425`.

[ERROR cargo_lipo] Failed to build "arti-orbot-ios" for "aarch64-apple-ios-sim": Executing "/Users/[redacted]/.rustup/toolchains/stable-aarch64-apple-darwin/bin/cargo" "--color" "auto" "build" "--manifest-path" "/Users/[redacted]/workspace/gp/orbot-ios/leaf-ffi-orbot/../arti-orbot-ios/Cargo.toml" "-p" "arti-orbot-ios" "--target" "aarch64-apple-ios-sim" "--lib" finished with error status: exit status: 101