Solved by josevalim in post #2 
              
              
                Mystery cracked, sorry for the noise: there is a second include directory at include/torch/csrc/api/include. We fixed it by doing: 
LIBTORCH_INCLUDE_PATH = $(LIBTORCH_DIR)/include/ $(LIBTORCH_DIR)/include/torch/csrc/api/include

I will be glad to send a PR to the docs if you think it is worth talkin…