Don't require one autograd backend's deps if building the other

Summary: Stop requiring CUDA if building the CPU backend, and stop requiring MKL/MKL-DNN if building the CUDA backend. Stop throwing if MKL-DNN components are missing - rely on `find_package_handle_standard_args`

Reviewed By: vineelpratap

Differential Revision: D13545117

fbshipit-source-id: 58409c657b952eb7205ba0574b00b338a890ed92

Author: jacobkahn

CMakeLists.txt

@@ -81,7 +81,7 @@ else()
 endif()
 
 # -------------------- Locate Backend-specific Dependencies --------------------
-find_package(CUDA 9.2) # CUDA 9.2 is required for >= ArrayFire 3.6.1
+find_package(CUDA 9.2 QUIET) # CUDA 9.2 is required for >= ArrayFire 3.6.1
 if (CUDA_FOUND)
   message(STATUS "CUDA found (library: ${CUDA_LIBRARIES} include: ${CUDA_INCLUDE_DIRS})")
 else()
@@ -101,7 +101,7 @@ else()
   endif ()
 endif()
 
-find_package(MKL)
+find_package(MKL QUIET)
 if (MKL_FOUND)
   message(STATUS "MKL found")
 else()
@@ -111,7 +111,7 @@ else()
   endif()
 endif()
 
-find_package(MKLDNN)
+find_package(MKLDNN QUIET)
 if (MKLDNN_FOUND)
   message(STATUS "MKLDNN found")
 else()

cmake/FindMKLDNN.cmake

@@ -16,7 +16,7 @@ set(MKLDNN_INCLUDE_DIR)
 find_package(BLAS)
 
 if (NOT MKL_FOUND)
-  message(FATAL_ERROR "Cannot build MKLDNN without MKL in current configuration.")
+  message(STATUS "Attempting to build MKLDNN without MKL in current configuration.")
   # TODO(@jacobkahn) support building MKLDNN with standalone Intel libmklml
 endif()
 
@@ -35,8 +35,7 @@ find_path(
 if (MKLDNN_INCLUDE_DIR)
   message(STATUS "MKLDNN headers found in ${MKLDNN_INCLUDE_DIR}")
 else()
-  message(FATAL_ERROR "MKLDNN headers not found; please set CMAKE_INCLUDE_PATH or
-MKLDNN_ROOT")
+  message(STATUS "MKLDNN headers not found; please set CMAKE_INCLUDE_PATH or MKLDNN_ROOT")
 endif()
 
 # Find library
@@ -54,8 +53,7 @@ find_library(
 if (MKLDNN_LIBRARY)
   message(STATUS "Using MKLDNN library found in ${MKLDNN_LIBRARY}")
 else()
-  message(FATAL_ERROR "MKLDNN library not found; please set CMAKE_LIBRARY_PATH o
-r MKLDNN_LIBRARY")
+  message(STATUS "MKLDNN library not found; please set CMAKE_LIBRARY_PATH or MKLDNN_LIBRARY")
 endif()
 
 set(MKLDNN_LIBRARIES ${MKLDNN_LIBRARY})