[MLton] MLton on intel mac

[Matthew Fluet]

>>> The changes I made will also align all C calls on x86 to 16 byte
>>> bounds.  I don't know enough about the frame layout within SML code
>>> to try this, but it doesn't seem to be necessary.
>>
>> It should be fairly easy to set things up to only do alignment to 16
>> byte boundaries on the MacOS.
>
> Technically, it's needed on other systems as well.  I believe
> GNU/Linux adopted a modified psABI which requires 16-byte alignment as
> well.  It's less apparent on these platforms because there is little
> SSE library code.

I guess its fine as long as it does no harm.  What I would be worried 
about is that extra, unexpected stack frame padding might mess up 
debugging with gdb (or some such).