Fix compilation error on unsupported target

Signed-off-by: Jiahao XU <[email protected]>

Author: NobodyXu

library/std/src/sys/anonymous_pipe/mod.rs

@@ -8,7 +8,7 @@
 //! # }
 //! ```
 
-use crate::{io, process::Stdio, sys::pipe::AnonPipe};
+use crate::{io, sys::pipe::AnonPipe};
 
 /// Create annoymous pipe that is close-on-exec and blocking.
 #[unstable(feature = "anonymous_pipe", issue = "127154")]

library/std/src/sys/anonymous_pipe/unix.rs

@@ -2,6 +2,7 @@ use super::*;
 
 use crate::{
     os::fd::{AsFd, AsRawFd, BorrowedFd, FromRawFd, IntoRawFd, OwnedFd, RawFd},
+    process::Stdio,
     sys::{
         fd::FileDesc,
         pipe::{anon_pipe, AnonPipe},

library/std/src/sys/anonymous_pipe/windows.rs

@@ -4,6 +4,7 @@ use crate::{
     os::windows::io::{
         AsHandle, AsRawHandle, BorrowedHandle, FromRawHandle, IntoRawHandle, OwnedHandle, RawHandle,
     },
+    process::Stdio,
     sys::{
         handle::Handle,
         pipe::{anon_pipe, AnonPipe, Pipes},

library/std/src/sys/pal/unsupported/pipe.rs

@@ -1,8 +1,16 @@
-use crate::io::{self, BorrowedCursor, IoSlice, IoSliceMut};
+use crate::{
+    fmt,
+    io::{self, BorrowedCursor, IoSlice, IoSliceMut},
+};
 
-#[derive(Debug)]
 pub struct AnonPipe(!);
 
+impl fmt::Debug for AnonPipe {
+    fn fmt(&self, _: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.0
+    }
+}
+
 impl AnonPipe {
     pub fn try_clone(&self) -> io::Result<Self> {
         self.0