Fix meta lib to be correctly compilable.

go/src/infra/gae/libs/meta/eg.go

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// +build appengine
+
 package meta
 
 import (
         "appengine/datastore"
 
         "infra/gae/libs/context"
         "infra/libs/errors"
 )
 
 var mark = errors.MakeMarkFn("eg")
@@ skipping 21 matching lines @@
         err := c.Get(egm)
         if err != datastore.ErrNoSuchEntity {
                 err = mark(err)
         } else {
                 // this is OK for callers. The version of the entity group is effectively 0
                 // in this case.
                 err = nil
         }
         return egm.Version, err
 }