Update clang to r339409b.

Change-Id: Ied8a188bb072c40035320acedc86164b66d920af
diff --git a/linux-x64/clang/include/llvm/ADT/SmallBitVector.h b/linux-x64/clang/include/llvm/ADT/SmallBitVector.h
index b639174..f86bebd 100644
--- a/linux-x64/clang/include/llvm/ADT/SmallBitVector.h
+++ b/linux-x64/clang/include/llvm/ADT/SmallBitVector.h
@@ -465,6 +465,11 @@
     return (*this)[Idx];
   }
 
+  // Push single bit to end of vector.
+  void push_back(bool Val) {
+    resize(size() + 1, Val);
+  }
+
   /// Test if any common bits are set.
   bool anyCommon(const SmallBitVector &RHS) const {
     if (isSmall() && RHS.isSmall())