Run unit test fails if set CMAKE_BUILD_TYPE to Debug

Steps to reproduce:

1. `cmake -DWITH_COVERAGE=ON -DCOVERALLS_UPLOAD=ON -DWITH_GPU=ON ..`
1. `make coveralls`

Note that `-DWITH_COVERAGE=ON`  will set CMAKE_BUILD_TYPE to `Debug` https://github.com/PaddlePaddle/Paddle/blob/develop/cmake/coveralls.cmake#L65