Rollup merge of rust-lang#85409 - CDirkx:cfg_redox, r=nagisa

Simplify `cfg(any(unix, target_os="redox"))` in example to just `cfg(unix)`

Update example for `OsString` that handled `redox` seperately from `unix`: Redox has been completely integrated under `target_family="unix"`, so `cfg(unix)` implies `target_os="redox"`

https://github.com/rust-lang/rust/blob/35dbef235048f9a2939dc20effe083ca483c37ff/compiler/rustc_target/src/spec/redox_base.rs#L26

Author: RalfJung

library/std/src/ffi/os_str.rs

@@ -601,7 +601,7 @@ impl OsStr {
     /// // sequences simply through collecting user command line arguments, for
     /// // example.
     ///
-    /// #[cfg(any(unix, target_os = "redox"))] {
+    /// #[cfg(unix)] {
     ///     use std::ffi::OsStr;
     ///     use std::os::unix::ffi::OsStrExt;
     ///