coroutines: Update tests for get-return-object errors.

We updated the handling of the errors for cases when the
ramp return cannot be constructed from the user's provided
get-return-object method.  This updates the testcases to
cover this.

gcc/testsuite/ChangeLog:

	* g++.dg/coroutines/void-gro-non-class-coro.C: Moved to...
	* g++.dg/coroutines/coro-bad-gro-01-void-gro-non-class-coro.C: ...here.
	* g++.dg/coroutines/coro-bad-gro-00-class-gro-scalar-return.C: New test.

(cherry picked from commit 2dbc16552204ffa28b643949eb1f26b787017b39)

gcc/testsuite/g++.dg/coroutines/coro-bad-gro-00-class-gro-scalar-return.C

+// Test handling of the case where we have a class g-r-o and a non-void
+// and non-class-type ramp return.
+
+#include "coro.h"
+
+int g_promise = -1;
+
+struct Thing {
+  double x;
+  Thing () : x(0.0) {}
+  ~Thing () {}
+};
+
+template<typename R, typename HandleRef, typename ...T>
+struct std::coroutine_traits<R, HandleRef, T...> {
+    struct promise_type {
+        promise_type (HandleRef h, T ...args)
+        { h = std::coroutine_handle<promise_type>::from_promise (*this);
+          PRINT ("Created Promise");
+          g_promise = 1;
+        }
+	~promise_type () { PRINT ("Destroyed Promise"); g_promise = 0;}
+        Thing get_return_object() { return {}; }
+
+        auto initial_suspend() {
+          return std::suspend_always{};
+         }
+        auto final_suspend() { return std::suspend_never{}; }
+
+        void return_void() {}
+        void unhandled_exception() {}
+    };
+};
+
+int
+my_coro (std::coroutine_handle<>& h)
+{
+  PRINT ("coro1: about to return");
+  co_return;
+} // { dg-error {'struct Thing' used where a 'int' was expected} }
+
+int main ()
+{
+  std::coroutine_handle<> h;
+  int t = my_coro (h);
+
+  if (h.done())
+    {
+      PRINT ("main: apparently was already done...");
+      abort ();
+    }
+
+  // initial suspend.
+  h.resume ();
+
+  // The coro should have self-destructed.
+  if (g_promise)
+    {
+      PRINT ("main: apparently we did not complete...");
+      abort ();
+    }
+
+  PRINT ("main: returning");
+  return t;
+}

gcc/testsuite/g++.dg/coroutines/void-gro-non-class-coro.C → gcc/testsuite/g++.dg/coroutines/coro-bad-gro-01-void-gro-non-class-coro.C

@@ -55,5 +55,5 @@ int main ()
     }
 
   PRINT ("main: returning");
-  return 0;
+  return t;
 }