Update cuvs to properly create a NCCL::NCCL target (rapidsai#720)

Previously cuvs was relying on the fact that nccl would be found when passed as `-lnccl` and be found on one of the implicit link directories.

Authors:
  - Robert Maynard (https://github.com/robertmaynard)

Approvers:
  - Divye Gala (https://github.com/divyegala)

URL: rapidsai#720

Author: robertmaynard

cpp/CMakeLists.txt

@@ -579,15 +579,22 @@ if(BUILD_SHARED_LIBS)
     )
 
     if(BUILD_MG_ALGOS)
-      set(CUVS_COMMS_DEPENDENCY nccl)
+      rapids_find_generate_module(
+        NCCL
+        HEADER_NAMES nccl.h
+        LIBRARY_NAMES nccl
+      )
+      find_package(NCCL REQUIRED)
+      target_link_libraries(cuvs_objs PRIVATE NCCL::NCCL)
+      target_link_libraries(cuvs PRIVATE NCCL::NCCL)
     endif()
 
     # Keep cuVS as lightweight as possible. Only CUDA libs and rmm should be used in global target.
     target_link_libraries(
       cuvs
       PUBLIC rmm::rmm raft::raft ${CUVS_CTK_MATH_DEPENDENCIES}
       PRIVATE nvidia::cutlass::cutlass $<TARGET_NAME_IF_EXISTS:OpenMP::OpenMP_CXX>
-              cuvs-cagra-search ${CUVS_COMMS_DEPENDENCY}
+              cuvs-cagra-search
     )
 
     if(NOT CUVS_COMPILE_DYNAMIC_ONLY)

cpp/tests/CMakeLists.txt

@@ -206,7 +206,8 @@ if(BUILD_TESTS)
 
   if(BUILD_MG_ALGOS)
     ConfigureTest(
-      NAME NEIGHBORS_MG_TEST PATH neighbors/mg/test_float.cu GPUS 1 PERCENT 100 ADDITIONAL_DEP nccl
+      NAME NEIGHBORS_MG_TEST PATH neighbors/mg/test_float.cu GPUS 1 PERCENT 100 ADDITIONAL_DEP
+      NCCL::NCCL
     )
   endif()