Don't neglect to "return *this".


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@165860 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/fstream b/include/fstream
index 7b6578f..1b8e7a0 100644
--- a/include/fstream
+++ b/include/fstream
@@ -344,6 +344,7 @@
 {
     close();
     swap(__rhs);
+    return *this;
 }
 
 #endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES