Build fails on CPU only machine

[arbellea]

Hi, I am trying to build this repo on a cpu only machine: I have torch 0.4 installed. I get the following error:

running build
running build_ext
building '_ext' extension
creating build
creating build/temp.linux-x86_64-3.7
creating build/temp.linux-x86_64-3.7/app
creating build/temp.linux-x86_64-3.7/app/detectors
creating build/temp.linux-x86_64-3.7/app/detectors/CenterNet
creating build/temp.linux-x86_64-3.7/app/detectors/CenterNet/src
creating build/temp.linux-x86_64-3.7/app/detectors/CenterNet/src/lib
creating build/temp.linux-x86_64-3.7/app/detectors/CenterNet/src/lib/models
creating build/temp.linux-x86_64-3.7/app/detectors/CenterNet/src/lib/models/networks
creating build/temp.linux-x86_64-3.7/app/detectors/CenterNet/src/lib/models/networks/DCNv2
creating build/temp.linux-x86_64-3.7/app/detectors/CenterNet/src/lib/models/networks/DCNv2/src
creating build/temp.linux-x86_64-3.7/app/detectors/CenterNet/src/lib/models/networks/DCNv2/src/cpu
g++ -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -fPIC -I/app/detectors/CenterNet/src/lib/models/networks/DCNv2/src -I/opt/anaconda3/envs/charts_main/lib/python3.7/site-packages/torch/lib/include -I/opt/anaconda3/envs/charts_main/lib/python3.7/site-packages/torch/lib/include/TH -I/opt/anaconda3/envs/charts_main/lib/python3.7/site-packages/torch/lib/include/THC -I/opt/anaconda3/envs/charts_main/include/python3.7m -c /app/detectors/CenterNet/src/lib/models/networks/DCNv2/src/vision.cpp -o build/temp.linux-x86_64-3.7/app/detectors/CenterNet/src/lib/models/networks/DCNv2/src/vision.o -DTORCH_EXTENSION_NAME=_ext -D_GLIBCXX_USE_CXX11_ABI=0 -std=c++11

cc1plus: warning: command line option ‘-Wstrict-prototypes’ is valid for C/ObjC but not for C++
In file included from /app/detectors/CenterNet/src/lib/models/networks/DCNv2/src/dcn_v2.h:3:0,
                 from /app/detectors/CenterNet/src/lib/models/networks/DCNv2/src/vision.cpp:2:
/app/detectors/CenterNet/src/lib/models/networks/DCNv2/src/cpu/vision.h:2:10: fatal error: torch/extension.h: No such file or directory
 #include <torch/extension.h>
          ^~~~~~~~~~~~~~~~~~~

It seems that it can't find torch/extension.h where could it be?