get_deref broken on Mac

[tcmulcahy]

@notgull the fix for get - bytecodealliance/rustix@10361e7 - also needs to be applied to get_deref.

The easiest way to repro is to change the xattr::get to xattr::get_deref in https://github.com/Stebalien/xattr/blob/master/tests/main.rs#L60

Test output:

---- test_path stdout ----
thread 'test_path' panicked at tests/main.rs:60:51:
called `Result::unwrap()` on an `Err` value: Os { code: 34, kind: Uncategorized, message: "Result too large" }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[Stebalien]

@tcmulcahy upstream fix is here: bytecodealliance/rustix#1045. Could you make a PR (here) with a failing regression test?