C++: Add DB scheme upgrade and downgrade scripts

Author: jketema

cpp/downgrades/34549c3b0937002f11037d01822ebe99442c1402/attribute_args.ql

@@ -0,0 +1,17 @@
+class AttributeArgument extends @attribute_arg {
+  string toString() { none() }
+}
+
+class Attribute extends @attribute {
+  string toString() { none() }
+}
+
+class LocationDefault extends @location_default {
+  string toString() { none() }
+}
+
+from AttributeArgument arg, int kind, Attribute attr, int index, LocationDefault location
+where
+  attribute_args(arg, kind, attr, index, location) and
+  not arg instanceof @attribute_arg_constant_expr
+select arg, kind, attr, index, location