[llvm] [OFFLOAD] Support host plugin on Windows (PR #180401)

[Alex Duran via llvm-commits]

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adurang wrote:

Support for ELF images has nothing to do with libffi support. It just happens than Windows doesn't support either. But, yes, let me fix it for Windows so it doesn't try to load images.

https://github.com/llvm/llvm-project/pull/180401