macOS build failure

[targos]

CI run: https://ci.nodejs.org/job/node-test-commit-osx/18665/nodes=osx1010/console

  g++ '-DV8_GYP_BUILD' '-DV8_TYPED_ARRAY_MAX_SIZE_IN_HEAP=0' '-D_DARWIN_USE_64_BIT_INODE=1' '-DV8_TARGET_ARCH_X64' '-DV8_EMBEDDER_STRING="-node.1"' '-DENABLE_DISASSEMBLER' '-DV8_PROMISE_INTERNAL_FIELD_COUNT' '-Dv8_promise_internal_field_count' '-DV8_INTL_SUPPORT' '-DV8_CONCURRENT_MARKING' '-DDISABLE_UNTRUSTED_CODE_MITIGATIONS' '-DANTLR4CPP_STATIC' -I../deps/v8/third_party/antlr4/runtime/Cpp/runtime/src -I../deps/v8/src/torque -I../deps/v8  -O3 -gdwarf-2 -fstrict-aliasing -mmacosx-version-min=10.7 -arch x86_64 -Wall -Wendif-labels -W -Wno-unused-parameter -std=gnu++1y -stdlib=libc++ -fno-threadsafe-statics -fno-strict-aliasing -MMD -MF /Users/iojs/build/workspace/node-test-commit-osx/nodes/osx1010/out/Release/.deps//Users/iojs/build/workspace/node-test-commit-osx/nodes/osx1010/out/Release/obj.host/torque/deps/v8/src/torque/ast-generator.o.d.raw   -c -o /Users/iojs/build/workspace/node-test-commit-osx/nodes/osx1010/out/Release/obj.host/torque/deps/v8/src/torque/ast-generator.o ../deps/v8/src/torque/ast-generator.cc
In file included from ../deps/v8/src/torque/ast-generator.cc:8:
In file included from ../deps/v8/src/torque/ast-generator.h:9:
In file included from ../deps/v8/src/torque/ast.h:14:
../deps/v8/src/torque/contextual.h:53:10: error: thread-local storage is not supported for the current target
  static thread_local VarType* top_;
         ^
../deps/v8/src/torque/contextual.h:57:1: error: thread-local storage is not supported for the current target
thread_local VarType* ContextualVariable<Derived, VarType>::top_ = nullptr;
^
2 errors generated.
make[2]: *** [/Users/iojs/build/workspace/node-test-commit-osx/nodes/osx1010/out/Release/obj.host/torque/deps/v8/src/torque/ast-generator.o] Error 1

[targos]

Should we update Xcode? /cc @nodejs/build

[mhdawson]

@gdams could you take a look into this? I wonder if its related to the version of Xcode or the target level of OSX.

[targos]

Discussion can happen in the V8 6.8 update thread: nodejs/node#21079

It is related to the version of Xcode. macOS 10.11 and 10.12 do not have this issue.