c++: Add unfixed test [PR88003]

Now that dg-ice is available, let's try it out.

gcc/testsuite/ChangeLog:

	PR c++/88003
	* g++.dg/cpp1y/auto-fn61.C: New test.

gcc/testsuite/g++.dg/cpp1y/auto-fn61.C

+// PR c++/88003
+// { dg-do compile { target c++14 } }
+// { dg-ice "poplevel_class" }
+
+auto test() {
+  struct O {
+    struct N;
+  };
+  return O();
+}
+
+typedef decltype(test()) TN;
+struct TN::N {};