[MLton] x86_64 merge

[Matthew Fluet]

>> 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).
>
> I agree.  I think that the way to go is to merge the runtime and basis
> library ASAP, then to continue x86_64 compiler work on the branch.
> That should make tracking easier, and start getting more feedback on
> the new runtime.

Sounds good.  Let's take care of revising the FFI with respect to bool 
before the merge.  I'd also like to make sure that the compiler bootstraps 
and passes regressions on Solaris and Cygwin.