Optimizing for lower calling overhead

[Samuel Crow]

EEC-Developers/eec#25 describes an optimization where the first pass of the compiler could keep track of which registers are used by a function and save only the non-scratch members of the register list to the stack in the function preamble and restore the same list at the end. Since it's 68k series only, I thought I'd mention it here also.

[phantasm4489]

I don't believe this issue affects e-vo