[REG 3.6 -> 4.0] Invalid warning about non-debug build when debugging Qt Quick UI

1. Install an official Qt package.
   An own release build of Qt might be sufficient, too, but I did not try that.
2. In Creator, configure a Kit using qmake from the Qt package.
3. Create a new Qt Quick UI project and configure it to use the kit from the previous step.
4. Run this project in the debugger.
   You'll see a warning that "This does not seem to be a 'Debug' build".

I'm not trying to Debug C++, so I think this warning is invalid. Creator 3.6 did not show it.

Found with Squish test tst_qml_js_console.