Issue description

Getting error C2370 when compiling as DLL.
For example:

error C2370: 'caffe2::FLAGS_caffe2_use_fatal_for_enforce': redefinition; different storage class

System Info

• PyTorch or Caffe2: C2
• How you installed PyTorch (conda, pip, source): source
• Build command you used (if compiling from source): cmake
• OS: Win10
• PyTorch version: master
• VS version (if compiling from source): 2017
• CMake version: 3.12