yes: Use pledge()

Userland/yes.cpp

@@ -25,9 +25,15 @@
  */
 
 #include <stdio.h>
+#include <unistd.h>
 
 int main(int argc, char** argv)
 {
+    if (pledge("stdio", nullptr) < 0) {
+        perror("pledge");
+        return 1;
+    }
+
     if (argc > 1) {
         for (;;) {
             puts(argv[1]);