message: Add test for posix_fadvise
diff: // ignore-windows: File handling is not implemented yet
  // compile-flags: -Zmiri-disable-isolation
  +#![feature(rustc_private)]
  +
  +extern crate libc;
  +
  use std::fs::{File, remove_file};
  use std::io::{Read, Write, ErrorKind, Result};
  +use std::os::unix::io::AsRawFd;
  use std::path::{PathBuf, Path};
  fn test_metadata(bytes: &[u8], path: &Path) -> Result<()> {
  @@ -40,6 +45,16 @@ fn main() {
  file.read_to_end(&mut contents).unwrap();
  assert_eq!(bytes, contents.as_slice());
  + // Test calling posix_fadvise on the file.
  + unsafe {
  + libc::posix_fadvise(
  + file.as_raw_fd(),
  + 0,
  + bytes.len() as i64,
  + libc::POSIX_FADV_DONTNEED,
  + );
  + }
  +
  // Test that metadata of an absolute path is correct.
  test_metadata(bytes, &path).unwrap();
  // Test that metadata of a relative path is correct.
  