C++: Add table for expanded compilation arguments

cpp/ql/lib/semmlecode.cpp.dbscheme

@@ -47,6 +47,19 @@ compilation_args(
     string arg : string ref
 );
 
+/**
+ * The expanded arguments that were passed to the extractor for a
+ * compiler invocation. This is similar to `compilation_args`, but
+ * for a `@someFile` argument, it includes the arguments from that
+ * file, rather than just taking the argument literally.
+ */
+#keyset[id, num]
+compilation_expanded_args(
+    int id : @compilation ref,
+    int num : int ref,
+    string arg : string ref
+);
+
 /**
  * Optionally, record the build mode for each compilation.
  */