message: Add definitions for unistd
diff: @@ -4,11 +4,26 @@ extern crate libc;
  use libc::*;
  +pub const NULL: c_int = 0;
  +
  pub const R_OK: c_int = 1;
  pub const W_OK: c_int = 2;
  pub const X_OK: c_int = 4;
  pub const F_OK: c_int = 8;
  +pub const SEEK_SET: c_int = 0;
  +pub const SEEK_CUR: c_int = 1;
  +pub const SEEK_END: c_int = 2;
  +
  +pub const F_ULOCK: c_int = 0;
  +pub const F_LOCK: c_int = 1;
  +pub const F_TLOCK: c_int = 2;
  +pub const F_TEST: c_int = 3;
  +
  +pub const STDIN_FILENO: c_int = 0;
  +pub const STDOUT_FILENO: c_int = 1;
  +pub const STDERR_FILENO: c_int = 2;
  +
  #[no_mangle]
  pub extern "C" fn _exit(status: c_int) {
  unimplemented!();
  