message: Check that fs errors have the proper kind
diff: // compile-flags: -Zmiri-disable-isolation
  use std::fs::{File, remove_file};
  -use std::io::{Read, Write};
  +use std::io::{Read, Write, ErrorKind};
  fn main() {
  let path = std::env::temp_dir().join("miri_test_fs.txt");
  @@ -23,8 +23,10 @@ fn main() {
  assert_eq!(bytes, contents.as_slice());
  // Removing file should succeed
  remove_file(&path).unwrap();
  - // Opening non-existing file should fail
  - assert!(File::open(&path).is_err());
  - // Removing non-existing file should fail
  - assert!(remove_file(&path).is_err());
  +
  + // The two following tests also check that the `__errno_location()` shim is working properly.
  + // Opening a non-existing file should fail with a "not found" error.
  + assert_eq!(ErrorKind::NotFound, File::open(&path).unwrap_err().kind());
  + // Removing a non-existing file should fail with a "not found" error.
  + assert_eq!(ErrorKind::NotFound, remove_file(&path).unwrap_err().kind());
  }
  