Declarative extensions won't show in Qt Creators designer if using Qt MinGW libraries

Qt Creator in the SDK is built with Microsoft compiler and the build key in Qt Creator's Ddesigner won't load plugins built with MinGW development libraries. This creates a situation where, when creating extension, the extension works as expected in Qmlviewer launched from Creator (play button) but will show the extensions as empty rectangles in designer.

To fix this issue either build Qt Creator coming with the SDK with MinGW, add error print into Qt Creator about the wrong build-key or bare minimum change the documentation to point out this issue.