Update clang to r339409.

Change-Id: I800772d2d838223be1f6b40d490c4591b937fca2
diff --git a/linux-x64/clang/include/llvm/Bitcode/BitstreamReader.h b/linux-x64/clang/include/llvm/Bitcode/BitstreamReader.h
index b484fa2..72e7619 100644
--- a/linux-x64/clang/include/llvm/Bitcode/BitstreamReader.h
+++ b/linux-x64/clang/include/llvm/Bitcode/BitstreamReader.h
@@ -429,7 +429,7 @@
     // don't care what code widths are used inside of it.
     ReadVBR(bitc::CodeLenWidth);
     SkipToFourByteBoundary();
-    unsigned NumFourBytes = Read(bitc::BlockSizeWidth);
+    size_t NumFourBytes = Read(bitc::BlockSizeWidth);
 
     // Check that the block wasn't partially defined, and that the offset isn't
     // bogus.