c backend

[Henry Cejtin]

I will raise my usual suggestion, which doesn't work all the time, but often
goes much farther than people think: use more than one process, one running
C code and one MLton.  Then you can use inter-process communication for
communication.  This doesn't work if huge amounts of data need to cross the
barrier relative to the amount of computation done, or if serializing that
data is very painful.  Still, it is easy and doesn't depend on any special
capabilities on either side.