Fix compilation of the doc tests on Windows.

Author: sunfishcode

library/std/src/os/fd/owned.rs

@@ -205,6 +205,7 @@ pub trait AsFd {
     /// ```rust,no_run
     /// use std::fs::File;
     /// # use std::io;
+    /// # #[cfg(any(unix, target_os = "wasi"))]
     /// # use std::os::fd::{AsFd, BorrowedFd};
     ///
     /// let mut f = File::open("foo.txt")?;

library/std/src/os/fd/raw.rs

@@ -42,6 +42,7 @@ pub trait AsRawFd {
     /// ```no_run
     /// use std::fs::File;
     /// # use std::io;
+    /// #[cfg(any(unix, target_os = "wasi"))]
     /// use std::os::fd::{AsRawFd, RawFd};
     ///
     /// let mut f = File::open("foo.txt")?;
@@ -80,6 +81,7 @@ pub trait FromRawFd {
     /// ```no_run
     /// use std::fs::File;
     /// # use std::io;
+    /// #[cfg(any(unix, target_os = "wasi"))]
     /// use std::os::fd::{FromRawFd, IntoRawFd, RawFd};
     ///
     /// let f = File::open("foo.txt")?;
@@ -115,6 +117,7 @@ pub trait IntoRawFd {
     /// ```no_run
     /// use std::fs::File;
     /// # use std::io;
+    /// #[cfg(any(unix, target_os = "wasi"))]
     /// use std::os::fd::{IntoRawFd, RawFd};
     ///
     /// let f = File::open("foo.txt")?;