Update clang to r339409.

Change-Id: I800772d2d838223be1f6b40d490c4591b937fca2
diff --git a/linux-x64/clang/include/llvm/ADT/CachedHashString.h b/linux-x64/clang/include/llvm/ADT/CachedHashString.h
index a56a621..d8f0e7a 100644
--- a/linux-x64/clang/include/llvm/ADT/CachedHashString.h
+++ b/linux-x64/clang/include/llvm/ADT/CachedHashString.h
@@ -43,6 +43,7 @@
   }
 
   StringRef val() const { return StringRef(P, Size); }
+  const char *data() const { return P; }
   uint32_t size() const { return Size; }
   uint32_t hash() const { return Hash; }
 };