[MLton] Cygwin, file open, and reserveEsp

[Matthew Fluet]

> > Doesn't the fact that the C back end works at least stronly imply that it
> > is a code generator bug in MLton?
>
> Yes, but mitigating against that is that the code from the native
> codegen works on Linux, even with -reserve-esp true.  And, this is
> Cygwin, which I don't trust.  I hope Matthew has some ideas when he
> gets back.

I don't really have any other ideas.  As Steve points out, the code
generator is pretty agnostic to the platform, except for reserveESP.  So,
the executed code should be identical on Linux (with -reserve-esp true)
and Cygwin.  I've never used the Cygwin port, so I don't really have any
idea of where to start.  But, I'm guessing that Steve did an strace to
find the failing system call, so the code up to that point is working.
Can we figure out what error is set?