Remove the DenseSet dependency from Sema.h.

llvm-svn: 112030
diff --git a/clang/lib/Sema/SemaLookup.cpp b/clang/lib/Sema/SemaLookup.cpp
index 0e6a6a4..8c8c007 100644
--- a/clang/lib/Sema/SemaLookup.cpp
+++ b/clang/lib/Sema/SemaLookup.cpp
@@ -26,6 +26,7 @@
 #include "clang/AST/ExprCXX.h"
 #include "clang/Basic/Builtins.h"
 #include "clang/Basic/LangOptions.h"
+#include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/Support/ErrorHandling.h"