Repository: pytorch
Issue: Build error: flat_hash_map.h(226) C2133
Labels: caffe2

## Issue description

When building the caffe2 on a Windows 10 using pytorch\scripts\biuld_windows.bat, 5 errors occurred:
```
       "C:\VS\Setup\pytorch\build\ALL_BUILD.vcxproj" (default target) (1) ->
       "C:\VS\Setup\pytorch\build\caffe2\caffe2.vcxproj" (default target) (5) ->
       "C:\VS\Setup\pytorch\build\caffe2\core\dispatch\dispatch.vcxproj" (default target) (9) ->
       (ClCompile target) ->
         C:\VS\Setup\pytorch\caffe2/utils/flat_hash_map/flat_hash_map.h(226): error C2133: 'public: static std::array<s
       ka::detailv3::sherwood_v3_entry_constexpr<`template-type-parameter-1'> const ,4> const ska::detailv3::EntryDefau
       ltTable<`template-type-parameter-1'>::table': unknown size (compiling source file C:\VS\Setup\pytorch\caffe2\cor
       e\dispatch\Dispatcher.cpp) [C:\VS\Setup\pytorch\build\caffe2\core\dispatch\dispatch.vcxproj]
         C:\VS\Setup\pytorch\caffe2/utils/flat_hash_map/flat_hash_map.h(226): error C2133: 'public: static std::array<s
       ka::detailv3::sherwood_v3_entry_constexpr<`template-type-parameter-1'> const ,4> const ska::detailv3::EntryDefau
       ltTable<`template-type-parameter-1'>::table': unknown size (compiling source file C:\VS\Setup\pytorch\caffe2\cor
       e\dispatch\OpSchemaRegistration.cpp) [C:\VS\Setup\pytorch\build\caffe2\core\dispatch\dispatch.vcxproj]
         C:\VS\Setup\pytorch\caffe2/utils/flat_hash_map/flat_hash_map.h(226): error C2133: 'public: static std::array<s
       ka::detailv3::sherwood_v3_entry_constexpr<`template-type-parameter-1'> const ,4> const ska::detailv3::EntryDefau
       ltTable<`template-type-parameter-1'>::table': unknown size (compiling source file C:\VS\Setup\pytorch\caffe2\cor
       e\dispatch\DispatchTable.cpp) [C:\VS\Setup\pytorch\build\caffe2\core\dispatch\dispatch.vcxproj]
         C:\VS\Setup\pytorch\caffe2/utils/flat_hash_map/flat_hash_map.h(226): error C2133: 'public: static std::array<s
       ka::detailv3::sherwood_v3_entry_constexpr<`template-type-parameter-1'> const ,4> const ska::detailv3::EntryDefau
       ltTable<`template-type-parameter-1'>::table': unknown size (compiling source file C:\VS\Setup\pytorch\caffe2\cor
       e\dispatch\KernelRegistration.cpp) [C:\VS\Setup\pytorch\build\caffe2\core\dispatch\dispatch.vcxproj]
         C:\VS\Setup\pytorch\caffe2/utils/flat_hash_map/flat_hash_map.h(226): error C2133: 'public: static std::array<s
       ka::detailv3::sherwood_v3_entry_constexpr<`template-type-parameter-1'> const ,4> const ska::detailv3::EntryDefau
       ltTable<`template-type-parameter-1'>::table': unknown size (compiling source file C:\VS\Setup\pytorch\caffe2\cor
       e\dispatch\TensorTypeIdRegistration.cpp) [C:\VS\Setup\pytorch\build\caffe2\core\dispatch\dispatch.vcxproj]
```

## Code example

Simply run the build_windows.bat as instructed on the website https://caffe2.ai/docs/getting-started.html?platform=windows&configuration=compile.

## System Info

- PyTorch or Caffe2: Caffe2
- How you installed PyTorch (conda, pip, source): source
- Build command you used (if compiling from source): build_windows.bat
- OS: Microsoft Windows 10 Pro
- Python version: 3.6
- CUDA/cuDNN version: 9.1.85
- GPU models and configuration: GPU 0: GeForce GPU
- GCC version (if compiling from source):
- CMake version: version 3.12.0-rc3
- Versions of any other relevant libraries: