Allow declaration of map and multimap iterator with incomplete mapped type. Patch from eugenis

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@231119 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/containers/associative/multimap/multimap.cons/default_recursive.pass.cpp

@@ -0,0 +1,29 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <map>
+
+// class multimap
+
+// multimap();
+
+#include <map>
+
+struct X
+{
+    std::multimap<int, X> m;
+    std::multimap<int, X>::iterator i;
+    std::multimap<int, X>::const_iterator ci;
+    std::multimap<int, X>::reverse_iterator ri;
+    std::multimap<int, X>::const_reverse_iterator cri;
+};
+
+int main()
+{
+}