[gn] Switch linux branch builder to gn

infra/mb/mb_config.pyl

 # Copyright 2016 The V8 project authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   # This is a map of buildbot master names -> buildbot builder names ->
   # config names (where each config name is a key in the 'configs' dict,
   # below). MB uses this dict to look up which config to use for a given bot.
   # Bots are ordered by appearance on waterfall.
   'masters': {
@@ skipping 99 matching lines @@
       'V8 Linux - s390x - sim': 'gyp_release_simulate_s390x',
       # X87.
       'V8 Linux - x87 - nosnap - debug builder':
           'gyp_debug_simulate_x87_no_snap',
     },
     'client.v8.branches': {
       'V8 Linux - beta branch': 'gn_release_x86',
       'V8 Linux - beta branch - debug': 'gn_debug_x86',
       'V8 Linux - stable branch': 'gn_release_x86',
       'V8 Linux - stable branch - debug': 'gn_debug_x86',
-      'V8 Linux64 - beta branch': 'gyp_release_x64',
+      'V8 Linux64 - beta branch': 'gn_release_x64',
       'V8 Linux64 - beta branch - debug': 'gn_debug_x64',
       'V8 Linux64 - stable branch': 'gn_release_x64',
       'V8 Linux64 - stable branch - debug': 'gn_debug_x64',
       'V8 arm - sim - beta branch': 'gyp_release_simulate_arm',
       'V8 arm - sim - beta branch - debug': 'gyp_debug_simulate_arm',
       'V8 arm - sim - stable branch': 'gyp_release_simulate_arm',
       'V8 arm - sim - stable branch - debug': 'gyp_debug_simulate_arm',
       'V8 mips64el - sim - beta branch': 'gyp_release_simulate_mips64el',
       'V8 mips64el - sim - stable branch': 'gyp_release_simulate_mips64el',
       'V8 mipsel - sim - beta branch': 'gyp_release_simulate_mipsel',
@@ skipping 530 matching lines @@
       'gn_args': 'target_cpu="x64"',
       'gyp_defines': 'target_arch=x64',
     },
 
     'x86': {
       'gn_args': 'target_cpu="x86"',
       'gyp_defines': 'target_arch=ia32',
     },
   },
 }