[PATCH] [zorg] Clean up libcxx-libcxxabi-singlethreaded-x86_64-linux-debian so that it passes the feature flags to lit

[Dan Albert]

================
Comment at: zorg/buildbot/builders/LibcxxAndAbiBuilder.py:70
@@ +69,3 @@
+    if additional_features:
+        litTestArgs = "--param=additional_features=" +
+                      ",".join(additional_features)
----------------
else this is undefined and then used below.

http://reviews.llvm.org/D5215