[Windows] Fix CUDA build by disabling ClangCL toolset for CUDA builds

[seyeong-han]

Questions

Does Windows 11 + Clang work? - setup.py

$ clang --version
clang version 19.1.5
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: C:\Program Files\Microsoft Visual Studio\2022\Professional\VC\Tools\Llvm\x64\bin

$ nvcc --version
nvcc: NVIDIA (R) Cuda compiler driver
Copyright (c) 2005-2025 NVIDIA Corporation
Built on Wed_Apr__9_19:29:17_Pacific_Daylight_Time_2025
Cuda compilation tools, release 12.9, V12.9.41
Build cuda_12.9.r12.9/compiler.35813241_0

Fix: windows + CUDA enforces to install cpu version of Torch

    if platform.system().lower() == "windows":
        # Try CUDA detection on Windows as well
        print("Windows detected, attempting CUDA detection...")
        try:
            cuda_version = _get_cuda_version(supported_cuda_versions)
            major, minor = cuda_version
            print(f"Detected CUDA version: {major}.{minor}")
            torch_url = _get_pytorch_cuda_url(cuda_version, torch_nightly_url_base)
            print(f"Using PyTorch URL: {torch_url}")
            return torch_url
        except Exception as err:
            print(f"CUDA detection failed ({err}), using CPU-only PyTorch")
            return f"{torch_nightly_url_base}/cpu"

Test Plan:

• Run .\install_executorch.bat on Windows with CUDA 12.9 installed
• Verify CMake configuration proceeds past CUDA compiler identification
• Verify non-CUDA builds still use ClangCL toolset

[pytorch-bot]

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As of commit 5573967 with merge base cea6be1 ():
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