Fixes [Bug 15960] YAMLTraits doesn't roundtrip on Windows.
Thanks to Kim Gräsman for help!


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@181699 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Format/Format.cpp b/lib/Format/Format.cpp
index 2f2f095..a62fa37 100644
--- a/lib/Format/Format.cpp
+++ b/lib/Format/Format.cpp
@@ -191,6 +191,7 @@
   // reference here.
   FormatStyle NonConstStyle = Style;
   Output << NonConstStyle;
+  Stream.flush();
   return Text;
 }