Implemented dependency tracking

tests/programs/function-pointer-field.q

@@ -1,4 +1,4 @@
-import core
+import sys
 
 struct Struct {
 	func *any
@@ -6,6 +6,11 @@ struct Struct {
 
 main() {
 	s := new(Struct)
-	s.func = core.exit
+	s.func = f
 	s.func()
+	sys.exit(1)
+}
+
+f() {
+	sys.exit(0)
 }

tests/programs/function-pointer.q

@@ -1,6 +1,13 @@
 import core
+import sys
 
 main() {
+	func := f
+	func()
+	sys.exit(1)
+}
+
+f() {
 	exit := core.exit
 	exit()
 }