Fix CUDNN location related build issue on Antergos Linux (based on Arch) (#24300)
Summary:
The issue is that `python setup.py install` will fail right at the end
of the build, with:
```
File "setup.py", line 380, in run
report('-- Detected cuDNN at ' + CUDNN_LIBRARY + ', ' + CUDNN_INCLUDE_DIR)
TypeError: must be str, not NoneType
```
This is due to `USE_CUDNN` being True, but CUDNN library and include dir
not being auto-detected. On this distro, the CUDA install goes into
`/opt/cuda/` while CUDNN goes into `/usr/lib`.
```
$ locate libcudnn.so
...
/usr/lib/libcudnn.so
/usr/lib/libcudnn.so.7
/usr/lib/libcudnn.so.7.6.1
$ locate libcublas.so # targets/... symlinked from /opt/cuda/lib64
...
/opt/cuda/targets/x86_64-linux/lib/libcublas.so
```
One could work around this by setting `CUDNN_LIB_DIR`, but that's
annoying and you only find out after running into this.
The path is added after `CUDA_HOME`, so should not be a problem on
systems which have multiple CUDA installs and select one via `CUDA_HOME`
Pull Request resolved: https://github.com/pytorch/pytorch/pull/24300
Differential Revision: D16839323
Pulled By: soumith
fbshipit-source-id: 5285fff604584ccfbe6368c5ee5a066f8fc10802
