Find RMM before CCCL (#20336)

Since #18235, cudf has not needed CCCL patches. However, that change missed reordering the `get_XXX` includes, so we have still always been cloning and using a separate CCCL version. Fix that by reordering. We also move the search for RMM before searching for NVTX since an RMM build can also supply that.

Authors:
  - Lawrence Mitchell (https://github.com/wence-)
  - Bradley Dice (https://github.com/bdice)

Approvers:
  - Bradley Dice (https://github.com/bdice)

URL: #20336

Author: wence-

cpp/CMakeLists.txt

@@ -279,10 +279,10 @@ include(cmake/thirdparty/get_nvtx.cmake)
 # find nvCOMP
 include(cmake/thirdparty/get_nvcomp.cmake)
 
-# find CCCL before rmm so that we get cudf's patched version of CCCL
+# find CCCL
 include(cmake/thirdparty/get_cccl.cmake)
 
-# find rmm
+# find rmm, should come after including CCCL to allow overriding the CCCL version used for testing
 include(cmake/thirdparty/get_rmm.cmake)
 
 # find croaring