Fix compile error in one of the runpipe tests with some gcc versions.

Author: meisterT

judge/runpipe_test/S_closes_stdin/judge.c

@@ -1,14 +1,23 @@
+#define _XOPEN_SOURCE 700
+
 #include <stdio.h>
 #include <signal.h>
+#include <unistd.h>
+#include <time.h>
 
 int main() {
   signal(SIGPIPE, SIG_IGN);
 
-  usleep(500000);
+  struct timespec req = {0};
+  req.tv_nsec = 500000000L; // 0.5 seconds
+  nanosleep(&req, NULL);
+
   printf("123\n");
   fflush(stdout);
   int x;
-  scanf("%d", &x);
+  if (scanf("%d", &x) != 1) {
+    return 1;
+  }
   if (x == 42)
     return 42;
   return 43;