Update NVBench build system with initial standalone support.

CMakeLists.txt

@@ -1,12 +1,22 @@
 # 3.18.3 is needed for a  MSVC + NVCC + C++17 bugfix.
 cmake_minimum_required(VERSION 3.18.3)
 
-project(nvbench CUDA)
+# CXX to work around issues with CUDA-only CMake projects.
+project(NVBench CUDA CXX)
+
+option(NVBench_ENABLE_TESTING "Build NVBench testing suite." OFF)
 
 # Setup some vars for CPM packages:
+list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules/")
+
+# NVBench requires C++17.
 set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CUDA_STANDARD 17)
 
+# TODO this probably should use GNUInstallDirs or something.
+set(NVBench_LIBRARY_OUTPUT_DIR "${CMAKE_BINARY_DIR}/lib")
+set(NVBench_EXECUTABLE_OUTPUT_DIR "${CMAKE_BINARY_DIR}/bin")
+
 include(CPM)
 
 CPMAddPackage(
@@ -16,4 +26,8 @@ CPMAddPackage(
 )
 
 add_subdirectory(nvbench)
-add_subdirectory(testing)
+
+if (NVBench_ENABLE_TESTING)
+  enable_testing()
+  add_subdirectory(testing)
+endif()