[Build] Fix cuda link target of cumem_allocator in CPU env

[guoyuhong]

FIX #12862

It looks like that the build system could not find -lcuda correctly in the CPU container.
list(APPEND CUMEM_LIBS cuda) is too simple for a CPU build env, ld cannot find the location. It is better to use CUDA::cuda_driver which is a full path.

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[guoyuhong]

@tlrmchlsmth do you some comments on this code change?

[tlrmchlsmth]

This seems reasonable to me -- @youkaichao WDYT?

[tlrmchlsmth]

Actually can we just delete this line completely? We have this link line in define_gpu_extension_target already:

vllm/cmake/utils.cmake

Lines 437 to 443 in 2ae8890

	# Don't use `TORCH_LIBRARIES` for CUDA since it pulls in a bunch of
	# dependencies that are not necessary and may not be installed.
	if (GPU_LANGUAGE STREQUAL "CUDA")
	target_link_libraries(${GPU_MOD_NAME} PRIVATE CUDA::cudart CUDA::cuda_driver)
	else()
	target_link_libraries(${GPU_MOD_NAME} PRIVATE ${TORCH_LIBRARIES})
	endif()

[guoyuhong]

Per my analysis, only when GPU_LANGUAGE STREQUAL "CUDA" the CUDA::cudart lib is linked in define_gpu_extension_target. However, the GPU_LANGUAGE for cumem_allocator is CXX. I think that is why extra libcuda is added to CUMEM_LIBS.

[tlrmchlsmth]

Thanks for the contribution! Verified that this doesn't break my existing build process. I also feel comfortable with the change as this is the official way to do it -see https://cmake.org/cmake/help/latest/module/FindCUDAToolkit.html.

Going to see if this avoids the ld issues that popped up when I tried #12424

[guoyuhong]

@tlrmchlsmth Thanks. I also tested whether we could remove this line of code. The building process was fine but there will be undefined symbol as follows.

[youkaichao]

LGTM, thanks for the fix!