Qt Maintenance Tool gives a long series of dialogs about XCode; can't quit

I was prompted to update, so I started that.

There's a very long series of dialogs that say such things as

You need to install Xcode version 8.2 (or newer) and set up Xcode command line tools. Download Xcode from https://developer.apple.com

and

You need to install Xcode version 5.0.0. Download Xcode from https://developer.apple.com/xcode

(but why would I have XCode 8.2 and 5.0 at the same time? that makes no sense.)

but each of them has only an OK button, not a Cancel.  If I hit OK, another dialog pops up... seemingly ad infinitum.  Maybe there should be a Cancel button, because even if I will update XCode right this instant, I will then need to restart the maintenance tool to get all the Qt updates, right?  so there's no point in continuing right now.

Also, I can't even quit.  If I right-click the icon on the dock and select Quit, it ignores that.  There is a Quit option in the MaintenanceTool menu, which it also ignores.

Given the fact that I can configure and build Qt on the command line, I think the XCode command line tools are actually installed.

So this bug needs several fixes, not just one:

1) add a cancel button (maybe)

2) ignoring Quit is completely unacceptable: must be fixed

3) why does it ask for two different XCode versions?

4) why does it fail to detect the XCode command line tools?

5) perhaps give a hint about what it's trying, how I can tell whether the XCode command line tools are really installed, and/or give me a command line or a description of how to install them?