Make non-exported symbols static in dllmain.c

[roflcopter4]

The PR I made last year was too big. I changed everything practically. Some changes were maybe valid, some not, but there were too many. So here's a little one that has mildly bothered me for months and months now. Nearly all of the (far too numerous) symbols in dllmain.c are not actually used outside that file. They can be static. I've made it so.

I also added void to a few function declarations with no parameters because I'm neurotic like that and renamed the variable Code to dllCode because it hurt me to look at, but I somehow avoided the urge to change anything else that might break something. So this shouldn't break anything, probably. Doesn't really fix anything either though.