A misspelled Cygwin-related path in my Windows PATH environment variable was
the apparent culprit. I had this:
PATH="d:\cygwn\bin;<Windows folders>;<other stuff>
After removing the Cygwin-related path element and restarting my system the PG
postmaster fired right up as a service.
My apologies to anyone who spent time trying to sort this out.
Regards,
Alder