typedef LLProcessLauncher::ll_pid_t to be HANDLE on Windows, pid_t elsewhere.
Then we can define getProcessID() returning ll_pid_t on all platforms,
retaining getProcessHandle() for hypothetical existing consumers... of which
there are none in practice.
This lets us define isRunning(ll_pid_t) to encapsulate the platform-specific
logic to actually check on a running child process, turning non-static
isRunning() into a fairly trivial wrapper.