On Windows, spawn(..., { detached: true }) prevents pwsh.exe (PowerShell) from
producing any stdout/stderr through pipe streams. This is because detached creates
a new process group which breaks pwsh's console host communication.
bash.exe and other cygwin/msys2 shells are unaffected by detached: true, but
they don't need it either -- on Windows, killProcessTree() already uses
taskkill /F /T /PID which kills the process tree by PID regardless of
whether the process was spawned detached.
The detached flag only matters on Unix, where kill(-pid, SIGKILL) requires a
process group that is only created via detached: true.
Fixes#4012
24dec9fcd5