Fix for CUDA ARCH case with no GPU

.github/workflows/windows.yml

@@ -50,7 +50,6 @@ jobs:
             CUDA_VERSION: 11.0.3
     env:
       BUILD_WEBRTC: ${{ ( matrix.BUILD_SHARED_LIBS == 'OFF' && matrix.STATIC_RUNTIME == 'ON' ) && 'ON' || 'OFF' }}
-      CUDAARCHS: 75     # Turing, oldest supported CUDA arch for CUDA v12. Required if no CUDA GPU on build machine.
 
     steps:
       - name: Disk space used

CMakeLists.txt

@@ -404,7 +404,7 @@ cmake_language(EVAL CODE "cmake_language(DEFER CALL open3d_patch_findthreads_mod
 if(BUILD_CUDA_MODULE)
     if(BUILD_COMMON_CUDA_ARCHS)
         if (CMAKE_CUDA_ARCHITECTURES)
-            message(STATUS "Building with user-provided architectures.")
+            message(STATUS "Building with user-provided architectures: ${CMAKE_CUDA_ARCHITECTURES}")
         else()
             # Build with all supported architectures for previous 2 generations and
             # M0 (minor=0) architectures for previous generations (including
@@ -424,11 +424,17 @@ if(BUILD_CUDA_MODULE)
             else()
                 set(CMAKE_CUDA_ARCHITECTURES 30-real 50-real 60-real 70-real 75)    # Kepler, Maxwell, Pascal, Turing
             endif()
+            message(STATUS "Using CUDA architectures: ${CMAKE_CUDA_ARCHITECTURES}")
         endif()
     else()
-        set(CMAKE_CUDA_ARCHITECTURES native)
+        execute_process(COMMAND nvidia-smi RESULT_VARIABLE HAVE_NVIDIA_GPU)
+        if (HAVE_NVIDIA_GPU)
+            message(STATUS "Building with native CUDA architecture.")
+            set(CMAKE_CUDA_ARCHITECTURES native)
+        else()
+            message(WARNING "No CUDA GPU detected. Building with default CUDA architecture.")
+        endif()
     endif()
-    message(STATUS "Using CUDA architectures: ${CMAKE_CUDA_ARCHITECTURES}")
     enable_language(CUDA)
     if (CMAKE_CUDA_COMPILER_ID STREQUAL "NVIDIA" AND CMAKE_CUDA_COMPILER_VERSION VERSION_LESS "10.1")
         message(FATAL_ERROR "CUDA 10.0 and older are not supported. Please upgrade to CUDA 10.1 or newer.")