message: add some missing assert_target_os
diff: @@ -197,12 +197,11 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
  fn nanosleep(
  &mut self,
  req_op: &OpTy<'tcx, Provenance>,
  - _rem: &OpTy<'tcx, Provenance>,
  + _rem: &OpTy<'tcx, Provenance>, // Signal handlers are not supported, so rem will never be written to.
  ) -> InterpResult<'tcx, i32> {
  - // Signal handlers are not supported, so rem will never be written to.
  -
  let this = self.eval_context_mut();
  + this.assert_target_os_is_unix("nanosleep");
  this.check_no_isolation("`nanosleep`")?;
  let duration = match this.read_timespec(&this.deref_operand(req_op)?)? {
  @@ -238,6 +237,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
  fn Sleep(&mut self, timeout: &OpTy<'tcx, Provenance>) -> InterpResult<'tcx> {
  let this = self.eval_context_mut();
  + this.assert_target_os("windows", "Sleep");
  this.check_no_isolation("`Sleep`")?;
  let timeout_ms = this.read_scalar(timeout)?.to_u32()?;
  