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

tests/string/strrchr.c

@@ -1,5 +1,6 @@
 #include <string.h>
 #include <stdio.h>
+#include <stdlib.h>
 
 int main(void) {
   char s0[] = "hello, world";
@@ -7,15 +8,15 @@ int main(void) {
   if (ptr != &s0[10]) {
     printf("%p != %p\n", ptr, &s0[10]);
     printf("strrchr FAIL , exit with status code %d\n", 1);
-    return 1;
+    return EXIT_FAILURE;
   }
   char s1[] = "";
   ptr = strrchr(s1, 'a');
   if (ptr != NULL) {
     printf("%p != 0\n", ptr);
     printf("strrchr FAIL, exit with status code %d\n", 1);
-    return 1;
+    return EXIT_FAILURE;
   }
   printf("strrch PASS, exiting with status code %d\n", 0);
-  return 0;
+  return EXIT_SUCCESS;
 }