message: simplify write_bytes() by using memory.write_repeat()
diff: @@ -405,13 +405,13 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
  "write_bytes" => {
  let u8 = self.tcx.types.u8;
  let ty = substs.type_at(0);
  + let ty_align = self.type_align(ty)?;
  + let val_byte = self.value_to_primval(arg_vals[1], u8)?.to_u128()? as u8;
  let size = self.type_size(ty)?.expect("write_bytes() type must be sized");
  - let mut ptr = arg_vals[0].read_ptr(&self.memory)?;
  + let ptr = arg_vals[0].read_ptr(&self.memory)?;
  let count = self.value_to_primval(arg_vals[2], usize)?.to_u64()?;
  - for _ in 0..(count * size) {
  - self.write_value_to_ptr(arg_vals[1], ptr, u8)?;
  - ptr = ptr.offset(1);
  - }
  + self.memory.check_align(ptr, size * count, ty_align)?;
  + self.memory.write_repeat(ptr, val_byte, size * count)?;
  }
  name => return Err(EvalError::Unimplemented(format!("unimplemented intrinsic: {}", name))),
  