Fixed dependency misconfiguration in Makefile

cpu/Makefile

@@ -1,4 +1,5 @@
-SOURCES=processor.v testbench.v memory.v
+SOURCES=processor.v testbench.v memory.v registers.v alu.v
+INCLUDES=proc_state_def.v
 VVP=processor.vvp
 
 .PHONY: run
@@ -13,8 +14,8 @@ wave: ${VVP}
 	vvp ${VVP} -lxt2
 	gtkwave test.lx2 gtkwave_savefile.gtkw
 
-${VVP} : ${SOURCES}
-	iverilog -g2012 $^ -o $@
+${VVP} : ${SOURCES} ${INCLUDES}
+	iverilog -g2012 ${SOURCES} -o $@
 
 .PHONY: clean
 clean: