[MLton] interrupted system call

[Henry Cejtin]

I don't know exactly what MLton does, but at the OS level, it depends on what
the sa_flags of the struct sigaction is set to.  If you want system calls  to
be  restarted  (after the signal handler is called) then you should set it to
SA_RESTART.  If you don't then as I recall Linux is more system-V-ish,  which
means that the system call fails with an errno as you see it.

The  notion  is that sometimes you want an interrupt to exit the system call,
and if you use SA_RESTART, then that  won't  happen,  although  you  can  use
setsetjmp and the like to get the effect (yuck).