tests: Portability fixes, replaced 0/1/-1 return codes with macros

tests/string/strtok.c

@@ -1,5 +1,6 @@
 #include <string.h>
 #include <stdio.h>
+#include <stdlib.h>
 
 int main(void) {
     char source[] = "I'd just like to interject for a moment.  What you're referring to as Linux, "
@@ -13,5 +14,5 @@ int main(void) {
         }
     }
 
-    return 0;
+    return EXIT_SUCCESS;
 }