C2PO: Fix test case to incur no warnings, besides for __goblint_check.

Author: jerhard

tests/regression/84-c2po/28-return-value.c

@@ -1,16 +1,35 @@
 // PARAM: --set ana.activated[+] c2po --set ana.activated[+] startState --set ana.activated[+] taintPartialContexts --set ana.c2po.askbase false
-int a, b, c;
-void *d(const *e) { return e + 200; }
-int *f() {}
-main() {
-  g(a, c, b);
-  if (0) {
-    __goblint_check(0); // NOWARN (unreachable)
-  }
-  __goblint_check(1); // reachable
+int a;
+
+struct h {
+  int c;
+};
+
+struct i {
+  int d;
+};
+
+struct h* b;
+struct i* c;
+
+const void *d(const int* e) {
+  return e + 200;
+}
+
+int *f() {
+  return (int*) 0;
 }
-g(int, struct h *, struct i *) {
+
+int g(int, struct h *, struct i *) {
   int *j = f();
   d(j);
   __goblint_check(1); // reachable
 }
+
+int main() {
+  g(a, b, c);
+  if (0) {
+    __goblint_check(0); // NOWARN (unreachable)
+  }
+  __goblint_check(1); // reachable
+}