raw_ostream: Forward declare OpenFlags and include FileSystem.h only where necessary.

llvm-svn: 207593

llvm/tools/llvm-extract/llvm-extract.cpp

@@ -22,6 +22,7 @@
 #include "llvm/IRReader/IRReader.h"
 #include "llvm/PassManager.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Support/FileSystem.h"
 #include "llvm/Support/ManagedStatic.h"
 #include "llvm/Support/PrettyStackTrace.h"
 #include "llvm/Support/Regex.h"