tidy-up: move literal to the right side of comparisons

Closes #17876

docs/examples/multithread.c

@@ -80,7 +80,7 @@ int main(void)
                                NULL, /* default attributes please */
                                pull_one_url,
                                (void *)urls[i]);
-    if(0 != error)
+    if(error)
       fprintf(stderr, "Couldn't run thread number %d, errno %d\n", i, error);
     else
       fprintf(stderr, "Thread %d, gets %s\n", i, urls[i]);