Mark functions not returning as sudo_noreturn

We also put NOTREACHED where it applies.

plugins/group_file/plugin_test.c

@@ -21,15 +21,16 @@
  * PVS-Studio Static Code Analyzer for C, C++ and C#: http://www.viva64.com
  */
 
-#include <stdio.h>
-#include <stdlib.h>
-#include <stdarg.h>
-#include <string.h>
-#include <unistd.h>
+#include <config.h>
 #include <ctype.h>
 #include <dlfcn.h>
 #include <errno.h>
 #include <limits.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
 
 #include "sudo_plugin.h"