Update clang to r339409b.

Change-Id: Ied8a188bb072c40035320acedc86164b66d920af
diff --git a/linux-x64/clang/lib64/cmake/llvm/LLVM-Config.cmake b/linux-x64/clang/lib64/cmake/llvm/LLVM-Config.cmake
index 8eabddc..474a874 100644
--- a/linux-x64/clang/lib64/cmake/llvm/LLVM-Config.cmake
+++ b/linux-x64/clang/lib64/cmake/llvm/LLVM-Config.cmake
@@ -302,7 +302,9 @@
     expand_topologically(${lib} "${required_libs}" "${visited_libs}")
   endforeach()
 
-  list(REVERSE required_libs)
+  if(required_libs)
+    list(REVERSE required_libs)
+  endif()
   set(${out_libs} ${required_libs} PARENT_SCOPE)
 endfunction()