Rework libcudf CMakeLists.txt to export targets for CPM (#7107)

These changes rework libcudf's CMakeLists.txt files to export targets for inclusion by other CMake projects. I took inspiration from [RMM's CMakeLists.txt](https://github.com/rapidsai/rmm/blob/branch-0.18/CMakeLists.txt). However I'm not a CMake expert, and likely missed/messed up a few things.

I also [fixed](0a8e80d) those annoying `-Wstrict-prototypes` warnings we see compiling Cython files.

These changes are adequate to build libcudf as a dependency in another CMake project with [CPM](https://github.com/TheLartians/CPM.cmake), for example:

```cmake
function(find_and_configure_cudf VERSION)

    include(get_cpm)

    CPMAddPackage(NAME  cudf
        VERSION         ${VERSION}
        GIT_REPOSITORY  https://github.com/trxcllnt/cudf.git
        # Can also use a local path to your repo clone for testing
        # GIT_REPOSITORY  /home/ptaylor/dev/rapids/cudf
        GIT_TAG         fix/cmake-exports
        GIT_SHALLOW     TRUE
        SOURCE_SUBDIR   cpp
        OPTIONS         "BUILD_TESTS OFF"
                        "BUILD_BENCHMARKS OFF"
                        "ARROW_STATIC_LIB ON"
                        "JITIFY_USE_CACHE ON"
                        "CUDA_STATIC_RUNTIME ON"
                        "DISABLE_DEPRECATION_WARNING ON"
                        # control where generated JIT headers get placed
                        # so we don't cache-bust ccache every clean build
                        "CUDF_GENERATED_INCLUDE_DIR ${CPM_SOURCE_CACHE}/cudf-build"
    )
endfunction()

find_and_configure_cudf(${CUDF_VERSION})

add_target(${PROJECT_NAME} SHARED "${src_files}")
target_link_libraries(${PROJECT_NAME} rmm::rmm cudf::cudf)
```

Authors:
  - Paul Taylor (@trxcllnt)
  - Robert Maynard (@robertmaynard)

Approvers:
  - Jake Hemstad (@jrhemstad)
  - Keith Kraus (@kkraus14)

URL: #7107

build.sh

@@ -150,24 +150,18 @@ if buildAll || hasArg libcudf; then
           -DCMAKE_INSTALL_PREFIX=${INSTALL_PREFIX} \
           ${CUDF_CMAKE_CUDA_ARCHITECTURES} \
           -DUSE_NVTX=${BUILD_NVTX} \
+          -DBUILD_TESTS=${BUILD_TESTS} \
           -DBUILD_BENCHMARKS=${BUILD_BENCHMARKS} \
           -DDISABLE_DEPRECATION_WARNING=${BUILD_DISABLE_DEPRECATION_WARNING} \
           -DPER_THREAD_DEFAULT_STREAM=${BUILD_PER_THREAD_DEFAULT_STREAM} \
           -DCMAKE_BUILD_TYPE=${BUILD_TYPE}
 
     cd ${LIB_BUILD_DIR}
-    if [[ ${INSTALL_TARGET} != "" ]]; then
-        cmake --build . -j${PARALLEL_LEVEL} --target install_cudf ${VERBOSE_FLAG}
-    else
-        cmake --build . -j${PARALLEL_LEVEL} --target cudf ${VERBOSE_FLAG}
-    fi
 
-    if [[ ${BUILD_TESTS} == "ON" ]]; then
-        cmake --build . -j${PARALLEL_LEVEL} --target build_tests_cudf ${VERBOSE_FLAG}
-    fi
+    cmake --build . -j${PARALLEL_LEVEL} ${VERBOSE_FLAG}
 
-    if [[ ${BUILD_BENCHMARKS} == "ON" ]]; then
-        cmake --build . -j${PARALLEL_LEVEL} --target build_benchmarks_cudf ${VERBOSE_FLAG}
+    if [[ ${INSTALL_TARGET} != "" ]]; then
+        cmake --build . -j${PARALLEL_LEVEL} --target install ${VERBOSE_FLAG}
     fi
 fi
 

cpp/cmake/Modules/ConfigureCUDA.cmake

@@ -14,10 +14,12 @@
 # limitations under the License.
 #=============================================================================
 
-# Auto-detect available GPU compute architectures
+# Find the CUDAToolkit
+find_package(CUDAToolkit REQUIRED)
 
-include(${CUDA_DATAFRAME_SOURCE_DIR}/cmake/Modules/SetGPUArchs.cmake)
-message(STATUS "CUDF: Building CUDF for GPU architectures: ${CMAKE_CUDA_ARCHITECTURES}")
+# Must come after find_package(CUDAToolkit) because we symlink
+# ccache as a compiler front-end for nvcc in gpuCI CPU builds.
+enable_language(CUDA)
 
 if(CMAKE_CUDA_COMPILER_VERSION)
   # Compute the version. from  CMAKE_CUDA_COMPILER_VERSION
@@ -30,32 +32,37 @@ message(VERBOSE "CUDF: CUDA_VERSION_MAJOR: ${CUDA_VERSION_MAJOR}")
 message(VERBOSE "CUDF: CUDA_VERSION_MINOR: ${CUDA_VERSION_MINOR}")
 message(STATUS "CUDF: CUDA_VERSION: ${CUDA_VERSION}")
 
+# Auto-detect available GPU compute architectures
+
+include(${CUDF_SOURCE_DIR}/cmake/Modules/SetGPUArchs.cmake)
+message(STATUS "CUDF: Building CUDF for GPU architectures: ${CMAKE_CUDA_ARCHITECTURES}")
+
 if(CMAKE_COMPILER_IS_GNUCXX)
-    string(APPEND CMAKE_CXX_FLAGS " -Wall -Werror -Wno-unknown-pragmas -Wno-error=deprecated-declarations")
+    list(APPEND CUDF_CXX_FLAGS -Wall -Werror -Wno-unknown-pragmas -Wno-error=deprecated-declarations)
     if(CUDF_BUILD_TESTS OR CUDF_BUILD_BENCHMARKS)
         # Suppress parentheses warning which causes gmock to fail
-        string(APPEND CMAKE_CUDA_FLAGS " -Xcompiler=-Wno-parentheses")
+        list(APPEND CUDF_CUDA_FLAGS -Xcompiler=-Wno-parentheses)
     endif()
 endif()
 
-string(APPEND CMAKE_CUDA_FLAGS " --expt-extended-lambda --expt-relaxed-constexpr")
+list(APPEND CUDF_CUDA_FLAGS --expt-extended-lambda --expt-relaxed-constexpr)
 
 # set warnings as errors
-string(APPEND CMAKE_CUDA_FLAGS " -Werror=cross-execution-space-call")
-string(APPEND CMAKE_CUDA_FLAGS " -Xcompiler=-Wall,-Werror,-Wno-error=deprecated-declarations")
+list(APPEND CUDF_CUDA_FLAGS -Werror=cross-execution-space-call)
+list(APPEND CUDF_CUDA_FLAGS -Xcompiler=-Wall,-Werror,-Wno-error=deprecated-declarations)
 
 if(DISABLE_DEPRECATION_WARNING)
-    string(APPEND CMAKE_CXX_FLAGS " -Wno-deprecated-declarations")
-    string(APPEND CMAKE_CUDA_FLAGS " -Xcompiler=-Wno-deprecated-declarations")
+    list(APPEND CUDF_CXX_FLAGS -Wno-deprecated-declarations)
+    list(APPEND CUDF_CUDA_FLAGS -Xcompiler=-Wno-deprecated-declarations)
 endif()
 
 # Option to enable line info in CUDA device compilation to allow introspection when profiling / memchecking
-if(CMAKE_CUDA_LINEINFO)
-    string(APPEND CMAKE_CUDA_FLAGS " -lineinfo")
+if(CUDA_ENABLE_LINEINFO)
+    list(APPEND CUDF_CUDA_FLAGS -lineinfo)
 endif()
 
 # Debug options
 if(CMAKE_BUILD_TYPE MATCHES Debug)
     message(VERBOSE "CUDF: Building with debugging flags")
-    string(APPEND CMAKE_CUDA_FLAGS " -G -Xcompiler=-rdynamic")
+    list(APPEND CUDF_CUDA_FLAGS -G -Xcompiler=-rdynamic)
 endif()

cpp/cmake/Modules/SetGPUArchs.cmake

@@ -35,27 +35,25 @@ if(CMAKE_CUDA_COMPILER_VERSION VERSION_LESS 9)
   list(REMOVE_ITEM SUPPORTED_CUDA_ARCHITECTURES "70")
 endif()
 
-if(${PROJECT_NAME}_BUILD_FOR_ALL_ARCHS)
-  set(CMAKE_CUDA_ARCHITECTURES ${SUPPORTED_CUDA_ARCHITECTURES})
-elseif(${PROJECT_NAME}_BUILD_FOR_DETECTED_ARCHS)
-  include(${PROJECT_SOURCE_DIR}/cmake/EvalGpuArchs.cmake)
+if(CUDF_BUILD_FOR_DETECTED_ARCHS)
+  include(${CUDF_SOURCE_DIR}/cmake/Modules/EvalGPUArchs.cmake)
   evaluate_gpu_archs(CMAKE_CUDA_ARCHITECTURES)
+  if(CMAKE_CUDA_ARCHITECTURES STREQUAL "ALL")
+    unset(CMAKE_CUDA_ARCHITECTURES CACHE)
+    set(CUDF_BUILD_FOR_ALL_ARCHS TRUE)
+  else()
+    set(CUDF_BUILD_FOR_ALL_ARCHS FALSE)
+    list(TRANSFORM CMAKE_CUDA_ARCHITECTURES APPEND "-real")
+  endif()
 endif()
 
-if (CMAKE_VERSION VERSION_GREATER_EQUAL 3.18)
+if(CUDF_BUILD_FOR_ALL_ARCHS)
+  set(CMAKE_CUDA_ARCHITECTURES ${SUPPORTED_CUDA_ARCHITECTURES})
   # CMake architecture list entry of "80" means to build compute and sm.
   # What we want is for the newest arch only to build that way
   # while the rest built only for sm.
   list(SORT CMAKE_CUDA_ARCHITECTURES ORDER ASCENDING)
   list(POP_BACK CMAKE_CUDA_ARCHITECTURES latest_arch)
   list(TRANSFORM CMAKE_CUDA_ARCHITECTURES APPEND "-real")
   list(APPEND CMAKE_CUDA_ARCHITECTURES ${latest_arch})
-else()
-  foreach(arch IN LISTS CMAKE_CUDA_ARCHITECTURES)
-    string(APPEND CMAKE_CUDA_FLAGS " -gencode=arch=compute_${arch},code=sm_${arch}")
-  endforeach()
-
-  list(GET CMAKE_CUDA_ARCHITECTURES -1 ptx)
-  string(APPEND CMAKE_CUDA_FLAGS " -gencode=arch=compute_${ptx},code=compute_${ptx}")
-  unset(CMAKE_CUDA_ARCHITECTURES)
 endif()