Dynamically generate arch struct

Now we don't need to hardcode the list of OS/Arch/Variant/Features in
android/arch.go.

Change-Id: I0f9cc35d55baa31f036825fdf5b9dd30d076e56e
diff --git a/android/module.go b/android/module.go
index aaaa2fb..8c48bd3 100644
--- a/android/module.go
+++ b/android/module.go
@@ -262,7 +262,7 @@
 	variableProperties      variableProperties
 	hostAndDeviceProperties hostAndDeviceProperties
 	generalProperties       []interface{}
-	archProperties          []*archProperties
+	archProperties          []interface{}
 	customizableProperties  []interface{}
 
 	noAddressSanitizer bool