Field layout in class Arguments is incompatible w\ 64-bit archs.

The length_ field must be defined as intptr_t rather than int.  This is
due to the fact that we place native argc/argv values into stack slots
(via SetFrameSlot) and then interpret the slots as a an instance of
Arguments class.

Little endian architectures get 'lucky' that the layout happens to work
with implicit padding.  Big endian is not as lucky.

See Runtime_ArrayConstructor for an example.

Based on
https://github.com/andrewlow/v8/commit/d8c3570f71c0be9914e79139740124bd1ca711a7