sim64 universal 64-bit cycle count support:

MaxCycleCount is accounted by countdown, eliminating the 1-instruction-overhead issue, and removing the need to compare against a growing TotalCycles.
Makes main.c responsible for counting total cycles, instead of 6502.c, so the size of MaxCycleCount etc. is fully determined in one location.
Makes error.c responsible for PrintCycles instead of paravirt.c, so that it can be treated globally instead of
Return value of main() should be SIM65_ERROR because it is unreachable by design.

src/sim65/6502.h

@@ -96,12 +96,6 @@ unsigned ExecuteInsn (void);
 ** executed instruction.
 */
 
-unsigned long GetCycles (void);
-/* Return the total number of clock cycles executed */
-
-extern int PrintCycles;
-/* flag to print cycles at program termination */
-
 
 /* End of 6502.h */