[MLton] new TextIO

[Henry Cejtin]

What I did was to take the top-level function I didn't want to be inlined
(say f) and simply add the following top-level code:

        val _ =
               if length (CommandLine.arguments ()) > 1000000
                  then (f some-arg; f some-arg; ...; f some-arg)
                  else ()

which should take some code space, and add a single test to the time, but
have no extra cost.