The flattened descendant list can contain a protected node (the
harness, on a Windows PID-reuse false-descendant) together with that
node's real children, collected by recursing through it. Skipping only
the exact protected pid kept omp alive but still TerminateProcess'd its
unrelated worker/tool subprocesses.
signal_tree/terminate_tree now drop every node whose recorded parent
chain within the enumerated set passes through a protected pid, so a
false descendant of the harness can no longer drag the harness's real
children into the kill set.
Fixes#7452
roboomp
e5f954b0fe