Update implementation of atomics with latest Chromium version but use compiler builtin atomics

src/v8.gyp

 # Copyright 2012 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 1763 matching lines @@
       'variables': {
         'optimize': 'max',
       },
       'include_dirs+': [
         '..',
       ],
       'sources': [
         'base/adapters.h',
         'base/atomic-utils.h',
         'base/atomicops.h',
-        'base/atomicops_internals_arm64_gcc.h',
-        'base/atomicops_internals_arm_gcc.h',
         'base/atomicops_internals_atomicword_compat.h',
-        'base/atomicops_internals_mac.h',
-        'base/atomicops_internals_mips_gcc.h',
-        'base/atomicops_internals_mips64_gcc.h',
-        'base/atomicops_internals_ppc_gcc.h',
-        'base/atomicops_internals_s390_gcc.h',
-        'base/atomicops_internals_tsan.h',
-        'base/atomicops_internals_x86_gcc.cc',
-        'base/atomicops_internals_x86_gcc.h',
+        'base/atomicops_internals_portable.h',
         'base/atomicops_internals_x86_msvc.h',
         'base/base-export.h',
         'base/bits.cc',
         'base/bits.h',
         'base/build_config.h',
         'base/compiler-specific.h',
         'base/cpu.cc',
         'base/cpu.h',
         'base/division-by-constant.cc',
         'base/division-by-constant.h',
@@ skipping 675 matching lines @@
       'conditions': [
         ['want_separate_host_toolset_mkpeephole==1', {
           'toolsets': ['host'],
         }, {
           'toolsets': ['target'],
         }],
       ],
     },
   ],
 }