Add missing flush call.  This is an attempt to fix a broken Windows buildbot.

llvm-svn: 146760
diff --git a/clang/lib/AST/APValue.cpp b/clang/lib/AST/APValue.cpp
index 0d4dea8..2a68341 100644
--- a/clang/lib/AST/APValue.cpp
+++ b/clang/lib/AST/APValue.cpp
@@ -480,6 +480,7 @@
   std::string Result;
   llvm::raw_string_ostream Out(Result);
   printPretty(Out, Ctx, Ty);
+  Out.flush();
   return Result;
 }