Fix doc test failures on Windows.

Author: sunfishcode

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

@@ -159,6 +159,7 @@ pub trait AsFd {
     /// # use std::os::unix::io::{AsFd, BorrowedFd};
     ///
     /// let mut f = File::open("foo.txt")?;
+    /// # #[cfg(any(unix, target_os = "wasi"))]
     /// let borrowed_fd: BorrowedFd<'_> = f.as_fd();
     /// # Ok::<(), io::Error>(())
     /// ```

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

@@ -40,6 +40,7 @@ pub trait AsRawFd {
     ///
     /// let mut f = File::open("foo.txt")?;
     /// // Note that `raw_fd` is only valid as long as `f` exists.
+    /// #[cfg(any(unix, target_os = "wasi"))]
     /// let raw_fd: RawFd = f.as_raw_fd();
     /// # Ok::<(), io::Error>(())
     /// ```
@@ -75,9 +76,11 @@ pub trait FromRawFd {
     /// use std::os::wasi::io::{FromRawFd, IntoRawFd, RawFd};
     ///
     /// let f = File::open("foo.txt")?;
+    /// # #[cfg(any(unix, target_os = "wasi"))]
     /// let raw_fd: RawFd = f.into_raw_fd();
     /// // SAFETY: no other functions should call `from_raw_fd`, so there
     /// // is only one owner for the file descriptor.
+    /// # #[cfg(any(unix, target_os = "wasi"))]
     /// let f = unsafe { File::from_raw_fd(raw_fd) };
     /// # Ok::<(), io::Error>(())
     /// ```
@@ -106,6 +109,7 @@ pub trait IntoRawFd {
     /// use std::os::wasi::io::{IntoRawFd, RawFd};
     ///
     /// let f = File::open("foo.txt")?;
+    /// #[cfg(any(unix, target_os = "wasi"))]
     /// let raw_fd: RawFd = f.into_raw_fd();
     /// # Ok::<(), io::Error>(())
     /// ```

library/std/src/os/windows/io/handle.rs

@@ -237,9 +237,10 @@ pub trait AsHandle {
     /// # Example
     ///
     /// ```rust,no_run
+    /// # #![feature(io_safety)]
     /// use std::fs::File;
     /// # use std::io;
-    /// use std::os::windows::{AsHandle, BorrowedHandle};
+    /// use std::os::windows::io::{AsHandle, BorrowedHandle};
     ///
     /// let mut f = File::open("foo.txt")?;
     /// let borrowed_handle: BorrowedHandle<'_> = f.as_handle();