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

llvm-svn: 207593
diff --git a/llvm/lib/MC/MCParser/AsmParser.cpp b/llvm/lib/MC/MCParser/AsmParser.cpp
index bad28ef..633d101 100644
--- a/llvm/lib/MC/MCParser/AsmParser.cpp
+++ b/llvm/lib/MC/MCParser/AsmParser.cpp
@@ -39,6 +39,7 @@
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/raw_ostream.h"
 #include <cctype>
+#include <deque>
 #include <set>
 #include <string>
 #include <vector>