Fix generator mismatch in cmakelists

Don't assume a multi-config subdir based on MSVC, instead gate on the generator used. Allows Ninja.

Author: JeodC

CMakeLists.txt

@@ -698,8 +698,9 @@ ExternalProject_Add(TorchExternal
     CMAKE_ARGS -DCMAKE_INSTALL_PREFIX=${CMAKE_BINARY_DIR}/Torch
 )
 ExternalProject_Get_Property(TorchExternal install_dir)
-if (MSVC)
-  set(TORCH_EXECUTABLE ${install_dir}/src/TorchExternal-build/$<CONFIGURATION>/torch)
+get_property(_is_multi_config GLOBAL PROPERTY GENERATOR_IS_MULTI_CONFIG)
+if (_is_multi_config)
+  set(TORCH_EXECUTABLE ${install_dir}/src/TorchExternal-build/$<CONFIG>/torch)
 else()
   set(TORCH_EXECUTABLE ${install_dir}/src/TorchExternal-build/torch)
 endif()