sl/tests: make the code compile with gcc-14.x

This commit fixes the following errors:
```
../tests/predator-regre/test-0170.c: In function 'DLInsertFirst':
../tests/predator-regre/test-0170.c:43:9: error: implicit declaration of function 'DLError' [-Wimplicit-function-declaration]
   43 |         DLError();
      |         ^~~~~~~

../tests/predator-regre/test-0183.c: In function 'main':
../tests/predator-regre/test-0183.c:114:5: error: implicit declaration of function '__VERIFIER_plot' [-Wimplicit-function-declaration]
  114 |     __VERIFIER_plot(NULL, &list, &p1, &p2);
      |     ^~~~~~~~~~~~~~~
[...]
```

Related: #92
Related: #93

tests/predator-regre/test-0170.c

@@ -36,7 +36,7 @@ void DLDisposeList (struct TList *L) {
     L->Act = ((void *)0);
     L->Last = ((void *)0);
 }
-
+void DLError(void);
 void DLInsertFirst (struct TList *L) {
     struct TNode * ptr = malloc(sizeof *ptr);
     if (((void *)0)==ptr) {

tests/predator-regre/test-0183.c

@@ -1,6 +1,6 @@
 #include <stdlib.h>
 
-extern int __VERIFIER_nondet_int(void);
+#include <verifier-builtins.h>
 
 static void fail(void) {
 ERROR:

tests/predator-regre/test-0184.c

@@ -1,6 +1,6 @@
 #include <stdlib.h>
 
-extern int __VERIFIER_nondet_int(void);
+#include <verifier-builtins.h>
 
 static void fail(void) {
 ERROR:

tests/predator-regre/test-0240.c

@@ -1,6 +1,6 @@
 #include <stdlib.h>
 
-extern int __VERIFIER_nondet_int(void);
+#include <verifier-builtins.h>
 
 struct node {
     struct node *next;