Update clang to r339409b.

Change-Id: Ied8a188bb072c40035320acedc86164b66d920af
diff --git a/linux-x64/clang/include/llvm/Support/FileOutputBuffer.h b/linux-x64/clang/include/llvm/Support/FileOutputBuffer.h
index ee8cbb7..68226ca 100644
--- a/linux-x64/clang/include/llvm/Support/FileOutputBuffer.h
+++ b/linux-x64/clang/include/llvm/Support/FileOutputBuffer.h
@@ -76,6 +76,10 @@
   /// deallocates the buffer and the target file is never written.
   virtual ~FileOutputBuffer() {}
 
+  /// This removes the temporary file (unless it already was committed)
+  /// but keeps the memory mapping alive.
+  virtual void discard() {}
+
 protected:
   FileOutputBuffer(StringRef Path) : FinalPath(Path) {}