Support autojit-device function and cuda.jit as cuda.autojit

See https://github.com/sklam/numba/blob/cuda_autojit_device/numba/cuda/tests/cudapy/test_cuda_autojit.py#L26 for example of the added feature
because "alwaysinline" (== forceinline) is used.
https://github.com/numba/numba/pull/863/files#diff-76fd867bea758e7aa376d2d50745ca05R228
see http://llvm.org/docs/LangRef.html#function-attributes