[gn] Add gn configs for mips to match old behavior

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 534 matching lines @@
       'gn_args': 'target_cpu="x86" v8_target_cpu="arm"',
       'gyp_defines': 'target_arch=ia32 v8_target_arch=arm',
     },
 
     'simulate_arm64': {
       'gn_args': 'target_cpu="x64" v8_target_cpu="arm64"',
       'gyp_defines': 'target_arch=x64 v8_target_arch=arm64',
     },
 
     'simulate_mipsel': {
-      'gn_args': 'target_cpu="x86" v8_target_cpu="mipsel"',
+      'gn_args':
+          'target_cpu="x86" v8_target_cpu="mipsel" mips_arch_variant="r2"',
       'gyp_defines': 'target_arch=ia32 v8_target_arch=mipsel',
     },
 
     'simulate_mips64el': {
       'gn_args': 'target_cpu="x64" v8_target_cpu="mips64el"',
       'gyp_defines': 'target_arch=x64 v8_target_arch=mips64el',
     },
 
     'simulate_ppc': {
       'gn_args': 'target_cpu="x86" v8_target_cpu="ppc"',
@@ skipping 114 matching lines @@
       'gn_args': 'target_cpu="x64"',
       'gyp_defines': 'target_arch=x64',
     },
 
     'x86': {
       'gn_args': 'target_cpu="x86"',
       'gyp_defines': 'target_arch=ia32',
     },
   },
 }