Minor cleanup of root CMakeLists.txt for better organization (#11988)

Cleanup  some minor issues in the root cudf CMakeLists.txt. Make the seaching for `CUDA_SANITIZER` only occur when we are building tests as that doesn't need to be done for production builds. 

Move the gdb pretty print script logic to a separate region to better document what it is for.

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

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

URL: #11988

cpp/CMakeLists.txt

@@ -124,12 +124,6 @@ rapids_find_package(
 )
 include(cmake/Modules/ConfigureCUDA.cmake) # set other CUDA compilation flags
 
-# ctest cuda memcheck
-find_program(CUDA_SANITIZER compute-sanitizer)
-set(MEMORYCHECK_COMMAND ${CUDA_SANITIZER})
-set(MEMORYCHECK_TYPE CudaSanitizer)
-set(CUDA_SANITIZER_COMMAND_OPTIONS "--tool memcheck")
-
 # ##################################################################################################
 # * dependencies ----------------------------------------------------------------------------------
 
@@ -738,6 +732,13 @@ add_library(cudf::cudftestutil ALIAS cudftestutil)
 if(CUDF_BUILD_TESTS)
   # include CTest module -- automatically calls enable_testing()
   include(CTest)
+
+  # ctest cuda memcheck
+  find_program(CUDA_SANITIZER compute-sanitizer)
+  set(MEMORYCHECK_COMMAND ${CUDA_SANITIZER})
+  set(MEMORYCHECK_TYPE CudaSanitizer)
+  set(CUDA_SANITIZER_COMMAND_OPTIONS "--tool memcheck")
+
   # Always print verbose output when tests fail if run using `make test`.
   list(APPEND CMAKE_CTEST_ARGUMENTS "--output-on-failure")
   add_subdirectory(tests)
@@ -762,11 +763,6 @@ if(CUDF_BUILD_BENCHMARKS)
   add_subdirectory(benchmarks)
 endif()
 
-# build pretty-printer load script
-if(Thrust_SOURCE_DIR AND rmm_SOURCE_DIR)
-  configure_file(scripts/load-pretty-printers.in load-pretty-printers @ONLY)
-endif()
-
 # ##################################################################################################
 # * install targets -------------------------------------------------------------------------------
 rapids_cmake_install_lib_dir(lib_dir)
@@ -930,3 +926,11 @@ add_custom_target(
   DEPENDS CUDF_DOXYGEN
   COMMENT "Custom command for building cudf doxygen docs."
 )
+
+# ##################################################################################################
+# * make gdb helper scripts ------------------------------------------------------------------------
+
+# build pretty-printer load script
+if(Thrust_SOURCE_DIR AND rmm_SOURCE_DIR)
+  configure_file(scripts/load-pretty-printers.in load-pretty-printers @ONLY)
+endif()