Well, I went to uninstall Xcode to start fresh and discovered the app wasn't even there at all. And I had no command line tools either. I love Macs, but sometimes stuff just seems to go poof...
I deleted the Developer folder and reinstalled Xcode and the command line tools. Then a fresh copy of qb64pe 4.0 happily compiled on my system - great! But...
@a740g - Yes, files with spaces in their names won't run and New programs without names won't run. If I open a New window and type in a few lines of code and then hit F5, the IDE only creates a start shell and an exe in the qb folder. If I then name and save that program, close the IDE and relaunch, then pressing F5 will run it.
Edit: Likewise, copy and pasted files won't run until they're saved and relaunched... And folders can't have spaces in their names either!
Thanks for all your effort, dev team.