[gn] Fix sysroot usage with gcc

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 407 matching lines @@
     'debug_trybot': {
       'mixins': ['debug_bot', 'minimal_symbols'],
     },
 
     'edge': {
       'gn_args': 'sanitizer_coverage_flags="edge"',
       'gyp_defines': 'sanitizer_coverage=edge',
     },
 
     'gcc': {
-      'gn_args': 'is_clang=false',
+      'gn_args': 'is_clang=false use_sysroot=false',
       'gyp_defines': 'clang=0',
     },
 
     'gcmole': {
       'gn_args': 'v8_gcmole=true',
       'gyp_defines': 'gcmole=1',
     },
 
     'gn': {'type': 'gn'},
 
@@ skipping 187 matching lines @@
       'gn_args': 'target_cpu="x64"',
       'gyp_defines': 'target_arch=x64',
     },
 
     'x86': {
       'gn_args': 'target_cpu="x86"',
       'gyp_defines': 'target_arch=ia32',
     },
   },
 }