Don't neglect to "return *this".

llvm-svn: 165860
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 88db3171dd5dcc54e3890b6f823c60831fc520a5
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