Fix compiler warning

src/sys_unix.c:132:10: warning: implicit conversion loses integer precision: 'long' to 'int' [-Wshorten-64-to-32]
        int r = lrand48(); // this is not thread-safe
            ~   ^~~~~~~~~

src/sys_unix.c

@@ -129,7 +129,7 @@ INTERNAL int SYS_RandomInt(void)
  // the casts are for the sake of clarity
  return (int)(ui & (unsigned int)INT_MAX);
 #else
- int r = lrand48(); // this is not thread-safe
+ int r = (int)lrand48(); // this is not thread-safe
  return r;
 #endif /* HAVE_GETRANDOM */
 }