Avoid fault in test desched_sigkill-no-syscallbuf.

This atomic_printf seem to change timing enough to
make this test less likely to fail.

Error message:
  FAILED at src/test/desched_sigkill.c:43: !(1 == read(parent_to_child[0], &ch, 1) && ch == 'x') errno:0 (Success)
  FAILED at src/test/desched_sigkill.c:43: !(1 == read(parent_to_child[0], &ch, 1) && ch == 'x') errno:0 (Success)
  FAILED at src/test/desched_sigkill.c:68: !(WIFSIGNALED(status) && WTERMSIG(status) == SIGKILL) errno:0 (Success)

Author: bernhardu

src/test/desched_sigkill.c

@@ -39,7 +39,9 @@ int main(void) {
   for (int i = 0; i < NUM_READERS; ++i) {
     pids[i] = fork();
     if (pids[i] == 0) {
+        atomic_printf("pid=%d :%d\n", getpid(), __LINE__);
         test_assert(1 == write(child_to_parent[1], "x", 1));
+        atomic_printf("pid=%d :%d\n", getpid(), __LINE__);
         test_assert(1 == read(parent_to_child[0], &ch, 1) && ch == 'x');
         pause();
         return 77;