[MLton] Intel Mac version of MLton

[Matthew Fluet]

> Is the x86 Mac version of MLton working well enough to actually use?

Not quite.  I'll check in the rest of Eric's patch, which uses two 
temporaries to handle stealing %esp from within inline assembly and 
16-byte aligning it.  That should make it useable, although I don't have 
a access to an Intel Mac to build the runtime constants or to compile 
the final code.