Rename _LIBCPP_DEBUG2 to _LIBCPP_DEBUG.

llvm-svn: 189140
diff --git a/libcxx/include/iterator b/libcxx/include/iterator
index bea09a6..52bc0de 100644
--- a/libcxx/include/iterator
+++ b/libcxx/include/iterator
@@ -321,7 +321,7 @@
 #include <Availability.h>
 #endif
 
-#ifdef _LIBCPP_DEBUG2
+#ifdef _LIBCPP_DEBUG
 #   include <__debug>
 #else
 #   define _LIBCPP_ASSERT(x, m) ((void)0)