Added support for building without MKL (facebookresearch#4147)

Summary: Pull Request resolved: facebookresearch#4147

Reviewed By: mnorris11

Differential Revision: D68790116

Pulled By: gtwang01

fbshipit-source-id: b0213913963991db6123e7f94e957f27d55ffa60

Author: stemann

CMakeLists.txt

@@ -62,6 +62,7 @@ option(FAISS_OPT_LEVEL "" "generic")
 option(FAISS_ENABLE_GPU "Enable support for GPU indexes." ON)
 option(FAISS_ENABLE_CUVS "Enable cuVS for GPU indexes." OFF)
 option(FAISS_ENABLE_ROCM "Enable ROCm for GPU indexes." OFF)
+option(FAISS_ENABLE_MKL "Enable MKL." ON)
 option(FAISS_ENABLE_PYTHON "Build Python extension." ON)
 option(FAISS_ENABLE_C_API "Build C API." OFF)
 option(FAISS_ENABLE_EXTRAS "Build extras like benchmarks and demos" ON)

faiss/CMakeLists.txt

@@ -372,7 +372,9 @@ target_link_libraries(faiss_avx512 PRIVATE OpenMP::OpenMP_CXX)
 target_link_libraries(faiss_avx512_spr PRIVATE OpenMP::OpenMP_CXX)
 target_link_libraries(faiss_sve PRIVATE OpenMP::OpenMP_CXX)
 
-find_package(MKL)
+if(FAISS_ENABLE_MKL)
+  find_package(MKL)
+endif()
 if(MKL_FOUND)
   target_link_libraries(faiss PRIVATE ${MKL_LIBRARIES})
   target_link_libraries(faiss_avx2 PRIVATE ${MKL_LIBRARIES})