Windows green battery: cli-selfhost + c-migrator + issue61 target cluster fails

[ropoctl]

On the Windows x86_64 self-host lane, bootstrap (seed→stage1→stage2→stage3) and fixpoint pass, but the build :test green battery fails on a cluster of self-host / migrator / regression targets. These have never passed on Windows. To keep the green battery green while they are fixed incrementally, they are gated off on Windows (if os() == "Windows": skip) and must be un-skipped one at a time.

Failing targets and observed symptom (from CI run 31973241915):

• cli-selfhost-smoke-tests — repl smoke failed, exit code -2 (lld-link non-standard .debug_abbrev section-name warning present)
• cli-selfhost-one-liner-tests — one-liner one-liner-e failed, exit code -2
• cli-selfhost-build-w-tests — build_w_not_ignored missing custom-build output
• cli-selfhost-project-tests — init_in_cwd file mismatch (missing out.default("init_in_cwd_case"))
• cli-selfhost-edge-tests — edge case prelude-output-functions failed, exit 1
• cli-selfhost-parallel-tests — exit code -267
• c-migrator-basic-tests — migrate-global-init-list failed, exit 1
• c-migrator-core-tests — migrate-libc-ctype failed, exit 1
• issue61-regression — could not copy src into repo fixture (Windows fs/path in the harness)

Several look like Windows path / process-spawn / fs-copy issues in the test harness rather than codegen (the compiler bootstraps + fixpoints cleanly). Each un-skip should root-cause its target.

Tracking the incremental un-skip. Each removal of a Windows gate here references this issue.