`gid_t` and `uid_t` aren't correct for Redox

According to the [source code](https://gitlab.redox-os.org/redox-os/relibc/-/blob/master/src/platform/types.rs?ref_type=heads#L64) for Redox:

```rust
pub type gid_t = c_int;
pub type uid_t = c_int;
```

however `libc` [defines them](https://github.com/rust-lang/libc/blob/main/src/unix/redox/mod.rs#L32) to be `u32`s:

```rust
pub type uid_t = u32;
pub type gid_t = u32;
```