Fix native CI waitpid assertion

[aaf2tbz]

Summary

Fix the C/C++/Obj-C CI failure in the runtime-routes test: the backend's process-wide SIGCHLD handler may reap a child before the test calls waitpid().

Changes

• Retry the test's child wait on EINTR and accept ECHILD when the handler already reaped it.
• Apply the helper to all three Wine-probe child waits in this test.

PR Readiness (MANDATORY)

• No hardcoded paths, secrets, or absolute /Users/... paths introduced
• Config/rules TOML validated if configs/mtsp-rules.toml or DLL maps changed
• Version metadata (CMakeLists.txt, app/src-c/Makefile, package.json, package-lock.json) in sync if version bumped
• Bottle/runtime migration and launch behavior preserved (rollback plan noted if changed)
• Docs / compatibility matrix updated for user-facing changes
• Regression test added for each bug fix

Validation

• make -C app/src-c test
• runtime-routes-test repeated five times
• Pre-commit clang-format --dry-run --Werror passed