message: implement write_bytes intrinsic
diff: @@ -402,6 +402,25 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
  }
  }
  + "write_bytes" => {
  + let u8 = self.tcx.types.u8;
  + let ty = substs.type_at(0);
  + let size = self.type_size(ty)?.expect("write_bytes() type must be sized");
  + let val_byte = self.value_to_primval(arg_vals[1], u8)?.to_u128()?;
  + let mut pattern: u128 = 0;
  + for ii in 0..size {
  + pattern |= val_byte << (8 * ii);
  + }
  + let val_full = Value::ByVal(PrimVal::from_u128(pattern));
  + let mut ptr = arg_vals[0].read_ptr(&self.memory)?;
  +
  + let count = self.value_to_primval(arg_vals[2], usize)?.to_u64()?;
  + for _ in 0..count {
  + self.write_value_to_ptr(val_full, ptr, ty)?;
  + ptr = ptr.offset(size);
  + }
  + }
  +
  name => return Err(EvalError::Unimplemented(format!("unimplemented intrinsic: {}", name))),
  }
  