The new class hold a list of ChildProcesses and periodically checks
their return value until they report termination. On Linux this check
is necessary to avoid leaving zombie processes behind.

- Also refactored internals to use weak/shared pointers

To prevent too much disruption to people who have our public projects as
part of their build or testing systems we are temporarily ignoring a
warning about using Xcode 15.

This allows real-time threads to join an audio workgroup on Apple platforms.