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

tests/math.c

@@ -1,9 +1,10 @@
 #include <math.h>
 #include <stdio.h>
+#include <stdlib.h>
 
 int main(void) {
     double pi = 3.14;
     float c = cos(pi);
     printf("cos(%f) = %f\n", pi, c);
-    return 0;
+    return EXIT_SUCCESS;
 }