Update clang to r339409b.

Change-Id: Ied8a188bb072c40035320acedc86164b66d920af
diff --git a/linux-x64/clang/include/llvm/MC/MCObjectStreamer.h b/linux-x64/clang/include/llvm/MC/MCObjectStreamer.h
index 035206d..c9e577b 100644
--- a/linux-x64/clang/include/llvm/MC/MCObjectStreamer.h
+++ b/linux-x64/clang/include/llvm/MC/MCObjectStreamer.h
@@ -179,7 +179,9 @@
   ///
   /// Emit the absolute difference between \c Hi and \c Lo, as long as we can
   /// compute it.  Currently, that requires that both symbols are in the same
-  /// data fragment.  Otherwise, do nothing and return \c false.
+  /// data fragment and that the target has not specified that diff expressions
+  /// require relocations to be emitted. Otherwise, do nothing and return
+  /// \c false.
   ///
   /// \pre Offset of \c Hi is greater than the offset \c Lo.
   void emitAbsoluteSymbolDiff(const MCSymbol *Hi, const MCSymbol *Lo,