Add missing include

clang/include/clang/Lex/MacroState.h

diff --git a/clang/include/clang/Lex/MacroState.h b/clang/include/clang/Lex/MacroState.h
index 2563b79..6f19e57 100644
--- a/clang/include/clang/Lex/MacroState.h
+++ b/clang/include/clang/Lex/MacroState.h
@@ -10,6 +10,7 @@
 #define LLVM_CLANG_LEX_MACROSTATE_H
 
 #include "clang/Lex/MacroInfo.h"
+#include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/PointerUnion.h"
 #include "llvm/ADT/TinyPtrVector.h"
 #include "llvm/Support/Allocator.h"