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/map/map.cons/default_recursive.pass.cpp

@@ -15,15 +15,15 @@
 
 #include <map>
 
-#if !__has_feature(cxx_noexcept)
-
 struct X
 {
     std::map<int, X> m;
+    std::map<int, X>::iterator i;
+    std::map<int, X>::const_iterator ci;
+    std::map<int, X>::reverse_iterator ri;
+    std::map<int, X>::const_reverse_iterator cri;
 };
 
-#endif
-
 int main()
 {
 }