possible incorrectness in libffi include dir assignment, doesn't seem impactful

This looks like an obvious mistake but I don't think it matters because the pkgconfig files are correct and provide the path ultimately:

https://github.com/codrsquad/portable-python/blob/89a620140f6f7bb066f77774c23187d78cf96275/src/portable_python/cpython.py#L142

            if self.active_module(LibFFI):
                yield f"LIBFFI_INCLUDEDIR={self.deps_lib}"

I'll refrain from opening a PR because I'm not sure... it's possible that this is necessary due to libffi nuances and just looks wrong, but there's no comment or commit message to indicate if thats the case.

阅读 src/portable_python/cpython.py 第 142 行，并将 LIBFFI_INCLUDEDIR 赋值与 issue 中提到的 libffi pkg-config 路径进行比较。检查该赋值是否会在 pkg-config 文件正确的情况下影响构建。如果仓库提供了针对性测试，则确认行为并使用该测试记录或修正差异后即视为完成。