Export NCCL dependency as part of raft::distributed. (#1077)

This is a follow-up to #1032 to include NCCL in raft::distributed so that all communications libraries are now cleanly encapsulated in a single interface dependency, allowing us to remove it from the raft-dask Python build and simplifying the process for other consumers.

Authors:
  - Vyas Ramasubramani (https://github.com/vyasr)

Approvers:
  - Robert Maynard (https://github.com/robertmaynard)
  - Corey J. Nolet (https://github.com/cjnolet)

URL: #1077

cpp/CMakeLists.txt

@@ -464,10 +464,20 @@ endif()
 
 set_target_properties(raft_distributed PROPERTIES EXPORT_NAME distributed)
 
+rapids_find_generate_module(
+  NCCL
+  HEADER_NAMES nccl.h
+  LIBRARY_NAMES nccl
+  BUILD_EXPORT_SET raft-distributed-exports
+  INSTALL_EXPORT_SET raft-distributed-exports
+)
+
 rapids_export_package(BUILD ucx raft-distributed-exports)
 rapids_export_package(INSTALL ucx raft-distributed-exports)
+rapids_export_package(BUILD NCCL raft-distributed-exports)
+rapids_export_package(INSTALL NCCL raft-distributed-exports)
 
-target_link_libraries(raft_distributed INTERFACE ucx::ucp)
+target_link_libraries(raft_distributed INTERFACE ucx::ucp NCCL::NCCL)
 
 # ##################################################################################################
 # * install targets-----------------------------------------------------------

python/raft-dask/raft_dask/common/CMakeLists.txt

@@ -12,10 +12,8 @@
 # the License.
 # =============================================================================
 
-include(${raft-dask-python_SOURCE_DIR}/cmake/thirdparty/get_nccl.cmake)
-
 set(cython_sources comms_utils.pyx nccl.pyx)
-set(linked_libraries raft::raft raft::distributed NCCL::NCCL)
+set(linked_libraries raft::raft raft::distributed)
 rapids_cython_create_modules(
   SOURCE_FILES "${cython_sources}" ASSOCIATED_TARGETS raft LINKED_LIBRARIES "${linked_libraries}"
                                                                             CXX