Add support for tvOS, watchOS and visionOS

[madsmtm]

By using cfg(target_vendor = "apple") instead of cfg(any(target_os = "macos", target_os = "ios")).

I suspect there may be a fairly large number of mach APIs which are likely to fail at runtime on these platforms - but that situation shouldn't be any different from iOS.

[madsmtm]

Looks like the ctest step failed because it doesn't understand cfg(target_vendor = "...") :/.

Options:

1. Remove the compile_error! altogether.
2. Try to make ctest pass --cfg ctest or similar, and place the cfg behind a cfg_attr.
3. Use cfg(any(target_os = "macos", target_os = "ios", target_os = "tvos", target_os = "watchos", target_os = "visionos")) (brittle IMO, Apple might very well introduce a new OS).

Let me know how you'd like me to proceed.

[JohnTitor]

Or, use a newer version of ctest, see rust-lang/libc#4655.
I haven't checked, but the crate has been rewritten completely, and the issue could be resolved in it (the old one uses quite old rustc and that's the cause).
I'll test it once it's published.

[JohnTitor]

I've tested but it'd take some more time to work without issues.
This PR itself doesn't have any issues so I'm going to merge, thanks for contributing and sorry for the delay!