Disabling benchmarks building by default. (#553)

This was an oversight because this will break all consumers downstream who are not explicitly turning this off in their `get_raft`. We should not build these by default (and we should eventually turn off compiling gtests by default as well).

Authors:
  - Corey J. Nolet (https://github.com/cjnolet)

Approvers:
  - Seunghwa Kang (https://github.com/seunghwak)

URL: #553

cpp/CMakeLists.txt

@@ -41,7 +41,7 @@ set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
 # - User Options  ------------------------------------------------------------
 
 option(BUILD_TESTS "Build raft unit-tests" ON)
-option(BUILD_BENCH "Build raft C++ benchmark tests" ON)
+option(BUILD_BENCH "Build raft C++ benchmark tests" OFF)
 option(CUDA_ENABLE_KERNELINFO "Enable kernel resource usage info" OFF)
 option(CUDA_ENABLE_LINEINFO "Enable the -lineinfo option for nvcc (useful for cuda-memcheck / profiler)" OFF)
 option(CUDA_STATIC_RUNTIME "Statically link the CUDA runtime" OFF)