Move gn secondary_source to the build/ directory

build/secondary/testing/gmock/BUILD.gn

 # Copyright (c) 2013 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.
 
 config("gmock_config") {
   # Gmock headers need to be able to find themselves.
   include_dirs = [ "include" ]
 }
 
 static_library("gmock") {
@@ skipping 25 matching lines @@
   direct_dependent_configs = [
     ":gmock_config",
     "//testing/gtest:gtest_config",
   ]
 }
 
 static_library("gmock_main") {
   sources = [ "src/gmock_main.cc" ]
   deps = [ ":gmock" ]
 }