message: avoid double negation
diff: @@ -15,7 +15,7 @@ use shims::time::system_time_to_duration;
  #[derive(Debug)]
  pub struct FileHandle {
  file: File,
  - read_only: bool,
  + writable: bool,
  }
  pub struct FileHandler {
  @@ -57,13 +57,13 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
  if (o_rdonly | o_wronly | o_rdwr) & !0b11 != 0 {
  throw_unsup_format!("Access mode flags on this platform are unsupported");
  }
  - let mut read_only = false;
  + let mut writable = true;
  // Now we check the access mode
  let access_mode = flag & 0b11;
  if access_mode == o_rdonly {
  - read_only = true;
  + writable = false;
  options.read(true);
  } else if access_mode == o_wronly {
  options.write(true);
  @@ -109,7 +109,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
  let fd = options.open(&path).map(|file| {
  let mut fh = &mut this.machine.file_handler;
  fh.low += 1;
  - fh.handles.insert(fh.low, FileHandle { file, read_only }).unwrap_none();
  + fh.handles.insert(fh.low, FileHandle { file, writable }).unwrap_none();
  fh.low
  });
  @@ -153,7 +153,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
  if let Some(handle) = this.machine.file_handler.handles.remove(&fd) {
  // We sync the file if it was opened in a mode different than read-only.
  - if !handle.read_only {
  + if handle.writable {
  // `File::sync_all` does the checks that are done when closing a file. We do this to
  // to handle possible errors correctly.
  let result = this.try_unwrap_io_result(handle.file.sync_all().map(|_| 0i32));
  @@ -164,7 +164,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
  } else {
  // We drop the file, this closes it but ignores any errors produced when closing
  // it. This is done because `File::sync_call` cannot be done over files like
  - // `/dev/urandom`. Check
  + // `/dev/urandom` which are read-only. Check
  // https://github.com/rust-lang/miri/issues/999#issuecomment-568920439 for a deeper
  // discussion.
  drop(handle);
  