Update xctoolchain to latest.

nlutsenko · nlutsenko · commit 35e965f2c50e · 2016-08-23T14:53:19.000-07:00
diff --git a/Vendor/xctoolchain b/Vendor/xctoolchain
@@ -1 +1 @@
-Subproject commit af8d7f69bf7a5b8e8edd94a139f83fc465b7b64a
+Subproject commit a66c63fe948cf8b4d77a51b69f35459fe0c68973
