cmCTestLaunch, which backs ctest --launch and ctest --instrument,
derived its exit code from the child's SpawnResult and ExitStatus but
ignored TermSignal. On POSIX a command killed by a signal reports
ExitStatus 0 and TermSignal N, so the launcher reported success for a
crashed or killed command, masking failed compile/link/custom rules on
the dashboard and in instrumentation snippets.
Classify the child with the ordered triple SpawnResult, TermSignal,
ExitStatus, mapping a signal-killed child to a non-zero exit code.
Native Windows is unaffected: abnormal termination already arrives as a
non-zero exit code there.
Fixes: #27921
Daksh Mamodiya
899e7231ab