Fix C++ API build work with libtorch (#1764)

CMakeLists.txt

 cmake_minimum_required(VERSION 2.8)
 project(torchvision)
 set(CMAKE_CXX_STANDARD 14)
+enable_language(CUDA)
+
+add_definitions(-D__CUDA_NO_HALF_OPERATORS__)
 
 find_package(Torch REQUIRED)
+find_package(pybind11 REQUIRED)
+
+include_directories(${PYTHON_INCLUDE_DIR})
 
-file(GLOB HEADERS torchvision/csrc/vision.h)
+file(GLOB HEADERS torchvision/csrc/*.h)
+file(GLOB CPU_HEADERS torchvision/csrc/cpu/vision_cpu.h)
+file(GLOB CPU_SOURCES torchvision/csrc/cuda/*.h torchvision/csrc/cpu/*.cpp)
+file(GLOB CUDA_HEADERS torchvision/csrc/cuda/vision_cuda.h)
+file(GLOB CUDA_SOURCES torchvision/csrc/cuda/*.h torchvision/csrc/cuda/*.cu)
 file(GLOB MODELS_HEADERS torchvision/csrc/models/*.h)
 file(GLOB MODELS_SOURCES torchvision/csrc/models/*.h torchvision/csrc/models/*.cpp)
 
-add_library (${PROJECT_NAME} SHARED ${MODELS_SOURCES})
+add_library (${PROJECT_NAME} SHARED ${MODELS_SOURCES} ${CPU_SOURCES} ${CUDA_SOURCES})
 target_link_libraries(${PROJECT_NAME} PUBLIC "${TORCH_LIBRARIES}")
 
 install(TARGETS ${PROJECT_NAME} DESTINATION ${CMAKE_INSTALL_PREFIX}/lib)
 install(FILES ${HEADERS} DESTINATION ${CMAKE_INSTALL_PREFIX}/include/${PROJECT_NAME})
+install(FILES ${CPU_HEADERS} DESTINATION ${CMAKE_INSTALL_PREFIX}/include/${PROJECT_NAME}/cpu)
+install(FILES ${CUDA_HEADERS} DESTINATION ${CMAKE_INSTALL_PREFIX}/include/${PROJECT_NAME}/cuda)
 install(FILES ${MODELS_HEADERS} DESTINATION ${CMAKE_INSTALL_PREFIX}/include/${PROJECT_NAME}/models)