Fix golden tests to use the "target" Bazel configuration (#581)

In practice, this means that `executable_semantics` will be built and run using the configuration specified on the command line, rather than e.g. always using `-c opt`.

Also fix a bug exposed by this change.

executable_semantics/interpreter/typecheck.cpp

@@ -149,8 +149,8 @@ auto TypeCheckExp(const Expression* e, TypeEnv types, Env values,
       return TCResult(new_e, t, types);
     }
     case ExpressionKind::Index: {
-      auto res = TypeCheckExp(e->GetFieldAccess().aggregate, types, values,
-                              nullptr, TCContext::ValueContext);
+      auto res = TypeCheckExp(e->GetIndex().aggregate, types, values, nullptr,
+                              TCContext::ValueContext);
       auto t = res.type;
       switch (t->tag) {
         case ValKind::TupleV: {