Correctly compile benchmarks (#7485)

The refactor in #7107 introduced two subtle bugs that caused benchmarks to not build correctly.

1. The `benchmark_main` target needs to be explicitly placed on the final executable link line as it injects object files, and that doesn't work via transitive propagation.
2. The variable names `BUILD_BENCHMARKS` and `BUILD_TESTING` are shared between RMM and CUDF. When CUDF builds RMM via CPM it will force cache these variables to `OFF`. This means that if a developer try to run `cmake -DBUILD_BENCHMARKS=ON .` any subsequent execution of just `cmake .` will cause CUDF to forget it should have kept benchmarks enabled.

Authors:
  - Robert Maynard (@robertmaynard)

Approvers:
  - Keith Kraus (@kkraus14)

URL: #7485

cpp/benchmarks/CMakeLists.txt

@@ -29,7 +29,6 @@ target_link_libraries(cudf_datagen
                       GTest::gmock_main
                       GTest::gtest_main
                       benchmark::benchmark
-                      benchmark::benchmark_main
                       Threads::Threads
                       cudf)
 
@@ -52,7 +51,8 @@ function(ConfigureBench CMAKE_BENCH_NAME)
     add_executable(${CMAKE_BENCH_NAME} ${ARGN})
     set_target_properties(${CMAKE_BENCH_NAME}
         PROPERTIES RUNTIME_OUTPUT_DIRECTORY "$<BUILD_INTERFACE:${CUDF_BINARY_DIR}/gbenchmarks>")
-    target_link_libraries(${CMAKE_BENCH_NAME} PRIVATE cudf_benchmark_common cudf_datagen)
+    target_link_libraries(${CMAKE_BENCH_NAME}
+        PRIVATE cudf_benchmark_common cudf_datagen benchmark::benchmark_main)
 endfunction()
 
 ###################################################################################################

cpp/cmake/thirdparty/CUDF_GetRMM.cmake

@@ -14,12 +14,26 @@
 # limitations under the License.
 #=============================================================================
 
-function(find_and_configure_rmm VERSION)
+function(cudf_save_if_enabled var)
+    if(CUDF_${var})
+        unset(${var} PARENT_SCOPE)
+        unset(${var} CACHE)
+    endif()
+endfunction()
 
+function(cudf_restore_if_enabled var)
+    if(CUDF_${var})
+        set(${var} ON CACHE INTERNAL "" FORCE)
+    endif()
+endfunction()
+
+function(find_and_configure_rmm VERSION)
     # Consumers have two options for local source builds:
     # 1. Pass `-D CPM_rmm_SOURCE=/path/to/rmm` to build a local RMM source tree
     # 2. Pass `-D CMAKE_PREFIX_PATH=/path/to/rmm/build` to use an existing local
     #    RMM build directory as the install location for find_package(rmm)
+    cudf_save_if_enabled(BUILD_TESTS)
+    cudf_save_if_enabled(BUILD_BENCHMARKS)
 
     CPMFindPackage(NAME rmm
         VERSION         ${VERSION}
@@ -32,6 +46,8 @@ function(find_and_configure_rmm VERSION)
                         "CMAKE_CUDA_ARCHITECTURES ${CMAKE_CUDA_ARCHITECTURES}"
                         "DISABLE_DEPRECATION_WARNING ${DISABLE_DEPRECATION_WARNING}"
     )
+    cudf_restore_if_enabled(BUILD_TESTS)
+    cudf_restore_if_enabled(BUILD_BENCHMARKS)
 
     if(NOT rmm_BINARY_DIR IN_LIST CMAKE_PREFIX_PATH)
         list(APPEND CMAKE_PREFIX_PATH "${rmm_BINARY_DIR}")

cpp/tests/CMakeLists.txt

@@ -35,8 +35,6 @@ target_compile_features(cudftestutil PUBLIC cxx_std_14 cuda_std_14)
 target_link_libraries(cudftestutil
                PUBLIC GTest::gmock
                       GTest::gtest
-                      GTest::gmock_main
-                      GTest::gtest_main
                       Threads::Threads
                       cudf)
 
@@ -55,7 +53,7 @@ function(ConfigureTest CMAKE_TEST_NAME )
     add_executable(${CMAKE_TEST_NAME} ${ARGN})
     set_target_properties(${CMAKE_TEST_NAME}
         PROPERTIES RUNTIME_OUTPUT_DIRECTORY "$<BUILD_INTERFACE:${CUDF_BINARY_DIR}/gtests>")
-    target_link_libraries(${CMAKE_TEST_NAME} PRIVATE cudftestutil)
+    target_link_libraries(${CMAKE_TEST_NAME} PRIVATE cudftestutil GTest::gmock_main GTest::gtest_main)
     add_test(NAME ${CMAKE_TEST_NAME} COMMAND ${CMAKE_TEST_NAME})
 endfunction()