Do not compile code with nvcc if no CUDA kernel exists

[gigony]

Currently, cuCIM code links CUDA runtime by creating PTX code explicitly (changing LANGUAGE to CUDA) even though cuCIM code (in C++) currently doesn't have any CUDA kernels.

# At least one file needs to be compiled with nvcc.
# Otherwise, it will cause `/usr/bin/ld: cannot find -lcudart` error message.
set_source_files_properties(src/cucim.cpp src/filesystem/cufile_driver.cpp PROPERTIES LANGUAGE CUDA)

That causes the issue with CuPy, causing the following error message (#170)

>>> import cupy as cp
>>> import cucim.clara
>>> a = cp.zeros((3,3))
...
cupy/cuda/memory.pyx in cupy.cuda.memory.Memory.__init__()

cupy_backends/cuda/api/runtime.pyx in cupy_backends.cuda.api.runtime.malloc()

cupy_backends/cuda/api/runtime.pyx in cupy_backends.cuda.api.runtime.check_status()

CUDARuntimeError: cudaErrorUnsupportedPtxVersion: the provided PTX was compiled with an unsupported toolchain.

The error is related to the nvcc version (from cuda 11.5) used in RAPIDS GPUCI.

https://docs.nvidia.com/cuda/cuda-runtime-api/group__CUDART__TYPES.html#group__CUDART__TYPES_1gg3f51e3575c21[…]e003844fd2df23a72a9ee7364d30150ae7e9e

cudaErrorUnsupportedPtxVersion = 222
This indicates that the provided PTX was compiled with an unsupported toolchain. The most common reason for this, is the PTX was generated by a compiler newer than what is supported by the CUDA driver and PTX JIT compiler.

With CUDA toolkit (nvcc) v11.4, it doesn't cause the error.

Fix the error by linking libcudart.so explicitly.
Also fixes warnings.

Close #170

[jakirkham]

rerun tests

[jakirkham]

There seem to be some test failures in this job, but they are coming from CuPy calls, which don't seem related to this change

[jakirkham]

After looking into this more, am thinking this failure may be related, but unclear how. Not seeing this failure in Greg's PR ( #172 ) and it is reproducing here. The CuPy error suggests it came up before CuPy was invoked. So the cause may be elsewhere. May need a more detailed traceback