Kits added by importing build directory don't have a debugger

1. Open a *.pro file for which Creator did not save a configuration yet.
2. Import a build of this project using a Qt version/kit which is not configured in Creator.
3. Configure the project like this.
4. Go to "Tools" -> "Options..." -> "Build & Run" -> "Kits".
   A new kit was added representing the Qt version/kit from step 2. This kit does not have a debugger.

Such automatically added kits should have a debugger whenever it's possible to guess one.