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

[via llvm-commits]

jeremyd2019 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
```

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