PR libstdc++/91871 fix Clang warnings in testsuite

	PR libstdc++/91871
	* testsuite/util/testsuite_hooks.h
	(conversion::iterator_to_const_iterator()): Do not return an invalid
	iterator. Test direct-initialization and direct-list-initialization
	as well as implicit conversion.

From-SVN: r276091

libstdc++-v3/ChangeLog

+2019-09-24  Jonathan Wakely  <jwakely@redhat.com>
+
+	PR libstdc++/91871
+	* testsuite/util/testsuite_hooks.h
+	(conversion::iterator_to_const_iterator()): Do not return an invalid
+	iterator. Test direct-initialization and direct-list-initialization
+	as well as implicit conversion.
+
 2019-09-23  Jonathan Wakely  <jwakely@redhat.com>
 
 	PR libstdc++/91788 (partial)

libstdc++-v3/testsuite/util/testsuite_hooks.h

@@ -326,13 +326,15 @@ namespace __gnu_test
       typedef typename _Container::const_iterator const_iterator;
 
       // Implicit conversion iterator to const_iterator.
-      static const_iterator
+      static void
       iterator_to_const_iterator()
       {
 	_Container v;
-	const_iterator it = v.begin();
-	const_iterator end = v.end();
-	return it == end ? v.end() : it;
+	const_iterator i __attribute__((unused)) = const_iterator(v.begin());
+	const_iterator j __attribute__((unused)) = true ? i : v.begin();
+#if __cplusplus >= 201103L
+	const_iterator k __attribute__((unused)) { v.begin() };
+#endif
       }
     };