[llvm] [LLVM] adjust lit.cfg.py for Cygwin (PR #151416)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

> With that `-elf` case switched on for cygwin and windows-cygnus, I get one test that doesn't fail anymore: `LLVM :: ExecutionEngine/MCJIT/stubs-sm-pic.ll` and these that now fail where they didn't before:
> 
> ```
>   LLVM :: ExecutionEngine/MCJIT/remote/cross-module-a.ll
>   LLVM :: ExecutionEngine/MCJIT/remote/multi-module-a.ll
>   LLVM :: ExecutionEngine/MCJIT/remote/simpletest-remote.ll
>   LLVM :: ExecutionEngine/MCJIT/remote/stubs-remote.ll
>   LLVM :: ExecutionEngine/MCJIT/remote/test-common-symbols-remote.ll
>   LLVM :: ExecutionEngine/MCJIT/remote/test-data-align-remote.ll
>   LLVM :: ExecutionEngine/MCJIT/remote/test-fp-no-external-funcs-remote.ll
>   LLVM :: ExecutionEngine/MCJIT/remote/test-global-init-nonzero-remote.ll
>   LLVM :: ExecutionEngine/MCJIT/remote/test-global-init-nonzero-sm-pic.ll
>   LLVM :: ExecutionEngine/MCJIT/remote/test-ptr-reloc-remote.ll
>   LLVM :: ExecutionEngine/MCJIT/remote/test-ptr-reloc-sm-pic.ll
> ```
> 
> These remote tests seem to all fail with:
> 
> ```
> Finalization error: could not register eh-frame: __register_frame function not found
> ```

All of those tests in the remote category are marked as XFAIL for Windows, see e.g. https://github.com/llvm/llvm-project/blob/llvmorg-22-init/llvm/test/ExecutionEngine/MCJIT/remote/cross-module-a.ll#L2 - this since 5bbf576945b77 and 4b6e021fad3188a12fcb8164b04780d7b3bef4c6 very very long ago.

And when actually running them, we hit this:
```
# .---command stderr------------
# | lli.exe: warning: host does not support external remote targets.
# | note: defaulting to local execution
# `-----------------------------
# error: command failed with exit status: 0xffffffff
```

So if I understand it correctly - enabling `-elf` fixes `ExecutionEngine/MCJIT/stubs-sm-pic.ll` (which also is failing on mingw, if the `-elf` addition is skipped), but it ends up breaking all the remote tests (which surprisingly were passing before, without `-elf`, and which never have worked on native windows).

https://github.com/llvm/llvm-project/pull/151416