Make example submissions work with modern gcc versions.

Tested with debian chroot oldstable, stable and testing.

Author: meisterT

example_problems/hello/submissions/no_output/test-compile-warning.c

@@ -6,6 +6,8 @@
 
 #include <stdio.h>
 
+char *gets(char *s);
+
 int main()
 {
 	char str[1000];

example_problems/hello/submissions/run_time_error/test-sigsegv.c

@@ -10,7 +10,7 @@ int main()
 	int a[10];
 	int *b;
 
-	b = 10;
+	b = (int *) 10;
 	*b = a[-1000000];
 
 	return 0;

example_problems/hello/submissions/time_limit_exceeded/stress-test-fork-setsid.c

@@ -13,6 +13,7 @@
  */
 
 #include <unistd.h>
+#include <stdlib.h>
 
 int main()
 {

example_problems/hello/submissions/time_limit_exceeded/test-fork.c

@@ -10,6 +10,7 @@
  */
 
 #include <unistd.h>
+#include <stdlib.h>
 
 int main()
 {

example_problems/hello/submissions/wrong_answer/test-cpu-pinning.c

@@ -7,6 +7,7 @@
  * @EXPECTED_RESULTS@: WRONG-ANSWER
  */
 
+#define _GNU_SOURCE
 #include <errno.h>
 #include <unistd.h>
 #include <sched.h>