Unbreak Debug build on Windows

llvm-svn: 187786

llvm/lib/Transforms/Utils/FlattenCFG.cpp

@@ -18,6 +18,7 @@
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 using namespace llvm;