For Android apps, we default to lowest available SDK version, even if it isn't supported

If you have installed e.g. Android SDK version 3, this will be the default for new Qt 5 projects. However, Qt 5 only supports version 9 and up, causing compile errors which are difficult to understand (missing headers that the app is not including itself.)

This is a fairly typical problem, so we should make sure we default to lowest available version >= 9.