layers: change android build to xml threading

Use threading validation layer generated from vk.xml for android.
diff --git a/layers/threading.cpp b/layers/threading.cpp
index 195f9e5..238cca7 100644
--- a/layers/threading.cpp
+++ b/layers/threading.cpp
@@ -29,7 +29,7 @@
 #include <list>
 using namespace std;
 
-#include "vk_layer.h"
+#include "vulkan/vk_layer.h"
 #include "vk_layer_config.h"
 #include "vk_layer_extension_utils.h"
 #include "vk_layer_utils.h"