Bug
PR #19792 merged recently (about half hour ago) breaks the build:

Environment
- PyTorch Version (e.g., 1.0): master
- OS (e.g., Linux): Ubuntu 18.04
- How you installed PyTorch (
conda, pip, source): source
- Build command you used (if compiling from source): cmake + ninja + gcc-8
- Python version: 3.6