nullary _prim's

[Matthew Fluet]

Steve,

Could you give a quick update on how we're dealing with nullary primitives
(things that are usually #define's)?  I was wading through compile.sml and
main.sml to get a compile which calls the x86-codegen functions, but I was
having a hard time getting something that didn't essentially need the
whole Main.commandLine function to compile.  As best I can make out, it's
doing a gcc call _before_ getting to the point of outputting the .c file.
So, I'm guessing that's the compile-time method of resolving primitives,
but I wasn't exactly clear on everything going on.