[MLton] MinGW done

[Matthew Fluet]

>> I think it makes sense to merge the refactored runtime and Basis Library
>> into HEAD in the near future.
>
> That seems like a good idea to me.  It's where most/all development is
> going on and it's stable enough to start living with on x86-linux.

I agree.  Especially now that there we've had some good contributions and 
improvements that, while prompted by the x86_64 changes, aren't directly 
related.

> Hopefully the other platforms will follow soon after the merge.  Plus,
> merging will save Matthew work in tracking changes to the trunk, and
> cut down on the chance for error there.

I think the question to be answered is how development should proceed 
after the merge of the runtime and Basis Library.  I suspect that the 
changes to the compiler proper will take some time; certainly, I found it 
convenient to checkpoint my progress with the runtime and Basis Library by 
committing changes that left the branch in a broken state.  So, if we 
merge and then continue development on both HEAD and the x86_64 branch, 
we'll still be tracking changes (though, I don't think that the compiler 
proper changes will require as extensive refactoring as the runtime and 
Basis Library, so tracking changes shouldn't be that difficult).