sim/rx: fill in missing 'void' for empty argument lists

sim/rx: fill in missing 'void' for empty argument lists

Ensure we have 'void' inside empty argument lists.  This was causing
several warnings for the rx simulator.

sim/rx/ChangeLog:

	* cpu.h (trace_register_changes): Add void parameter type.
	* err.c (ee_overrides): Likewise.
	* mem.c (mem_usage_stats): Likewise.
	(e): Likewise.
	* reg.c (stack_heap_stats): Likewise.
	* rx.c (pop): Likewise.
	(poppc): Likewise.
	(decode_opcode): Likewise.
	* syscalls.c (arg): Likewise.