BufRead doctets: avoid Miri failure on Windows due to missing FS support

Author: RalfJung

library/std/src/io/mod.rs

@@ -2335,6 +2335,7 @@ pub trait BufRead: Read {
     /// #![feature(buf_read_has_data_left)]
     /// use std::io;
     /// use std::io::prelude::*;
+    /// # if cfg!(all(miri, windows)) { return; } // FIXME(miri-windows-file-access)
     ///
     /// let stdin = io::stdin();
     /// let mut stdin = stdin.lock();