[MLton] x86_64 merge

[Stephen Weeks]

> 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.