Add fake definitions for Windows

Author: LinkTed

library/std/src/sys/unix/ext/net/ancillary.rs

@@ -11,6 +11,16 @@ use crate::sys::net::Socket;
 
 #[cfg(any(target_os = "android", target_os = "linux",))]
 use libc::{gid_t, pid_t, uid_t};
+// FIXME(#43348): Make libc adapt #[doc(cfg(...))] so we don't need these fake definitions here?
+#[cfg(not(unix))]
+#[allow(non_camel_case_types)]
+mod libc {
+    pub struct ucred;
+    pub struct cmsghdr;
+    pub type pid_t = i32;
+    pub type gid_t = u32;
+    pub type uid_t = u32;
+}
 
 pub(super) fn recv_vectored_with_ancillary_from(
     socket: &Socket,