[MLton] MinGW hosted MLton

[Stephen Weeks]

> I thought OS_PROCESS_EXTRA was exported somewhere, that's why I left
> it. 

The warning message guaranteed us that wait was unused.

> I switched to using system() b/c there is no /bin/sh on windows. :-)
> 
> If you read the manpage for system() it says that SIGCHLD will be blocked
> and SIGINT and SIGQUIT will be ignored. I presume that SML/NJ was trying to
> fake a proper system call. However, since we are using a real system call
> now, I don't think that it is necessary to do this ourselves...?

OK.

> Under windows, of course, this is all irrelevant as there are no
> signals.  (That's why I don't/can't use protect in the
> waitpid->cwait method...)

OK.  I changed the definition of protect so that it does nothing on
Windows, which makes the definition of reap cleaner.