Import prebuilt clang toolchain for linux.
diff --git a/linux-x64/clang/include/llvm/ADT/StringSet.h b/linux-x64/clang/include/llvm/ADT/StringSet.h
new file mode 100644
index 0000000..9af44c0
--- /dev/null
+++ b/linux-x64/clang/include/llvm/ADT/StringSet.h
@@ -0,0 +1,52 @@
+//===- StringSet.h - The LLVM Compiler Driver -------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open
+// Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+//  StringSet - A set-like wrapper for the StringMap.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_STRINGSET_H
+#define LLVM_ADT_STRINGSET_H
+
+#include "llvm/ADT/StringMap.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/Allocator.h"
+#include <cassert>
+#include <initializer_list>
+#include <utility>
+
+namespace llvm {
+
+  /// StringSet - A wrapper for StringMap that provides set-like functionality.
+  template <class AllocatorTy = MallocAllocator>
+  class StringSet : public StringMap<char, AllocatorTy> {
+    using base = StringMap<char, AllocatorTy>;
+
+  public:
+    StringSet() = default;
+    StringSet(std::initializer_list<StringRef> S) {
+      for (StringRef X : S)
+        insert(X);
+    }
+
+    std::pair<typename base::iterator, bool> insert(StringRef Key) {
+      assert(!Key.empty());
+      return base::insert(std::make_pair(Key, '\0'));
+    }
+
+    template <typename InputIt>
+    void insert(const InputIt &Begin, const InputIt &End) {
+      for (auto It = Begin; It != End; ++It)
+        base::insert(std::make_pair(*It, '\0'));
+    }
+  };
+
+} // end namespace llvm
+
+#endif // LLVM_ADT_STRINGSET_H