Description

This PR resolves two important issues in the setsid utility to align it with standard POSIX and GNU behaviors and improve robustness:

1. POSIX/GNU Standard Exit Statuses:
   • Updates report_failure_to_exec to correctly map command execution failures. If the command was not found (ErrorKind::NotFound), it yields 127. For all other failures (e.g. PermissionDenied or general execution failures), it maps to the standard exit code 126 (instead of leaving it at 0).
2. Robust Signal Termination Handling:
   • Safe-guards child.wait() in spawn_command. Previously, calling unwrap() on status.code() would cause setsid to panic if the child process was terminated by a signal.
   • We now check if status.code() returns None. If it was terminated by a signal, we use std::os::unix::process::ExitStatusExt's signal() to retrieve the signal and calculate the standard exit status as 128 + signal.

Changes

• src/uu/setsid/src/setsid.rs: Modified report_failure_to_exec and spawn_command.
• tests/by-util/test_setsid.rs: Added the fork_wait_returns_signal_exit_code integration test to verify the exit status under signal termination (using sh -c "kill -s INT $$" which terminates with SIGINT (2) and yields 130).

Verification

• Running cargo test --test tests setsid passes successfully.