Regression in 0.12.0: wrong architecture selected when building for Python x86 on Windows x64 host

### Description After upgrading from `scikit-build-core 0.11.6` to `0.12.0`, building a package that targets **Python 3.13 x86 (win32)** on a **Windows x64 host** fails with a linker architecture mismatch. The build was working correctly with `0.11.6`. This appears to be a regression introduced by the cross-compilation changes in #1050 (`Better support for cross-compilation`) and/or #1196 (`Respect _PYTHON_HOST_PLATFORM env variable`). ### Environment - **scikit-build-core**: 0.12.0 (regression), works on 0.11.6 - **CMake**: 3.31.6 - **MSVC**: 19.44.35222.0 (Visual Studio 17 2022) - **Python**: 3.13.12 x86 (`C:\hostedtoolcache\windows\Python\3.13.12\x86`) - **Host OS**: Windows (GitHub Actions `windows-latest` / `windows-2025`) - **Package being built**: `h3==4.3.0` (uses scikit-build-core as build backend) ### Steps to reproduce 1. Use GitHub Actions `windows-latest` runner 2. Install Python 3.13 x86 (`architecture: x86` in `actions/setup-python`) 3. Attempt to build `h3==4.3.0` from source using `uv sync` or `pip install` ### Error ``` -- Building for: Visual Studio 17 2022 -- Check for working C compiler: C:/Program Files/Microsoft Visual Studio/2022/Enterprise/VC/Tools/MSVC/14.44.35207/bin/Hostx64/x64/cl.exe warning LNK4272: library machine type 'x86' conflicts with target machine type 'x64' fatal error LNK1120: 190 unresolved externals ``` CMake correctly detects Python as x86: ``` -- Found Python: ...\Python\3.13.12\x86\python.exe (found version "3.13.12") ``` But selects `Hostx64/x64/cl.exe` instead of the x86 compiler, causing the linker to fail when linking against `python313.lib` (x86). ### Expected behavior scikit-build-core should select the correct x86 toolchain when the target Python is x86, as it did in 0.11.6. ### Workaround Pinning `scikit-build-core` to `0.11.6` via uv's `extra-build-dependencies`: ```toml [tool.uv.extra-build-dependencies] h3 = ["scikit-build-core==0.11.6"] ```