CMake check for FAISS use in benchmarks (rapidsai#1591)

CUVS_ANN_BENCH_USE_FAISS is now set to OFF if all relevant flags are set OFF.

The status is reported in the cmake log:
-- Finding or building hnswlib
-- Checking for FAISS use in benchmarks...
-- CUVS_ANN_BENCH_USE_FAISS is OFF

closes rapidsai#1590.

Authors:
  - https://github.com/irina-resh-nvda

Approvers:
  - Tamas Bela Feher (https://github.com/tfeher)

URL: rapidsai#1591

Author: irina-resh-nvda

cpp/bench/ann/CMakeLists.txt

@@ -51,7 +51,29 @@ option(CUVS_KNN_BENCH_USE_CUVS_BRUTE_FORCE "Include cuVS brute force knn in benc
 
 find_package(Threads REQUIRED)
 
-set(CUVS_ANN_BENCH_USE_FAISS ON)
+# ----- FAISS use in Benchmarks ----
+get_cmake_property(_variableNames VARIABLES)
+
+set(CUVS_ANN_BENCH_USE_FAISS OFF)
+message(STATUS "Checking for FAISS use in benchmarks...")
+foreach(_varName ${_variableNames})
+  if(_varName MATCHES "CUVS_ANN_BENCH_USE_FAISS.+")
+    if(${_varName})
+      set(CUVS_ANN_BENCH_USE_FAISS ON)
+      message(STATUS "${_varName} is detected as ON.")
+      break()
+    endif()
+  endif()
+endforeach()
+
+if(CUVS_ANN_BENCH_USE_FAISS)
+  message(STATUS "CUVS_ANN_BENCH_USE_FAISS is switched ON")
+else()
+  message(STATUS "CUVS_ANN_BENCH_USE_FAISS is switched OFF")
+endif()
+
+# ----------------------------------
+
 set(CUVS_FAISS_ENABLE_GPU ON)
 set(CUVS_USE_FAISS_STATIC ON)