Wasmer: LLVM backend not available anymore in Windows builds

[mhonert]

Describe the bug

The LLVM backend is not available anymore in the Windows build of Wasmer version 0.17.1.

Steps to reproduce

Run wasmer.exe using the --backend llvm option.

Expected behavior

Wasmer uses the LLVM backend.

Actual behavior

Wasmer prints the following error message:

error: 'llvm' isn't a valid value for '--backend <backend>'
        [possible values: auto, cranelift]

Additional context

In version 0.16.2 the LLVM backend was still available.

[MarkMcCaskey]

Looking at CI, this does not seem to be resolved yet on master https://github.com/wasmerio/wasmer/runs/1153060407?check_suite_focus=true .

@nlewycky if you have context here, perhaps you know what's going on. I'm unclear on whether this is an issue with our CI or with the LLVM backend.

[nlewycky]

LLVM+JIT hasn't been made to work on Windows yet. It should be pretty close now given that LLVM+native cross-compilation on linux targeting windows works.