J3 user app demo

Hello 地平线专家：

3.当前天工开物版本：1.27.

4.问题定位：编译错误

5.开发的demo/案例：

当前想跑一个user_app main.cc demo，目前编译时候报错如下：

-- The C compiler identification is GNU 6.5.0

-- The CXX compiler identification is GNU 6.5.0

-- Check for working C compiler: /opt/gcc-linaro-6.5.0-2018.12-x86_64_aarch64-linux-gnu/bin/aarch64-linux-gnu-gcc

-- Check for working C compiler: /opt/gcc-linaro-6.5.0-2018.12-x86_64_aarch64-linux-gnu/bin/aarch64-linux-gnu-gcc -- works

-- Detecting C compiler ABI info

-- Detecting C compiler ABI info - done

-- Detecting C compile features

-- Detecting C compile features - done

-- Check for working CXX compiler: /opt/gcc-linaro-6.5.0-2018.12-x86_64_aarch64-linux-gnu/bin/aarch64-linux-gnu-g++

-- Check for working CXX compiler: /opt/gcc-linaro-6.5.0-2018.12-x86_64_aarch64-linux-gnu/bin/aarch64-linux-gnu-g++ -- works

-- Detecting CXX compiler ABI info

-- Detecting CXX compiler ABI info - done

-- Detecting CXX compile features

-- Detecting CXX compile features - done

-- Build type: Release

CMake Error at CMakeLists.txt:33 (target_link_libraries):

Cannot specify link libraries for target "user_app" which is not built by

this project.

-- Configuring incomplete, errors occurred!

See also "/root/ddk/samples/solution_zoo/solution_example/xxxx_example/build_arm/CMakeFiles/CMakeOutput.log".

make: *** No targets specified and no makefile found. Stop.