* Add the check for whether CUDA Driver and NVRTC is available for the runtime system.

* Call cuInit to initialize the CUDA Driver API before all CUDA callings.
test=develop

* Change the behavior when libnvrtc.so can not be found, printing a warning instead of exiting.
test=develop

* Do not initialize CUDA Driver API for windows and macos.
test=develop

* Remove the call of cuInit when entering paddle and enable the test_code_generator.
test=develop

* Add some built-in functions for __half.
test=develop

* Change save_intermediate_out to false in unittest.
test=develop

* Fix error reference to tempropary variable when seting including path for device_code.
test=develop