[MLton] cvs commit: Added PosixError.SysCall structure.

[Matthew Fluet]

> > Note, unfortunately, if an ML handled signal arrives while the signals are
> > blocked, unblocking the signals don't seem to deliver those signals.  So,
> > we might miss some signals here.
>
> Odd.  I'm 99% sure the OS is supposed to hold onto the signals and
> deliver them when the program unblocks.

Maybe; I didn't have code that demonstrated it.  It's just not clearly
spelled out for me in the man pages.