[MLton] bool array size

[Stephen Weeks]

> Is there some other reason for making bool = int, which is I guess
> what you're doing? C89 doesn't have boolean type .. you can use
> 'char' is you like. Why choose int?

No good reason.  It's what we initially choose for our first codegen
back in 1998 and it hasn't gotten changed since.  Matthew is currently
overhauling the FFI as part of the 64-bit port -- once that's done I
assume it will be easy to make SML bool equal to whatever C type we
want.