presets: Detect abnormal termination of workflow step commands

If the command for a step (cmake, ctest, or cpack) terminates abnormally,
libuv sets the exit code to 0 and reports the process termination signal
in a separate struct member. That carries through to the structure we use
to track the process and ultimately give back to the workflow step loop.
Don't rely on the exit code alone to test for failure, also check for spawning
errors and abnormal termination too.

Fixes: #27273