Consider build below source valid for latest Qmake

This shows "Qmake does not support build directories below the source
directory." only when using Qmake/Kit older than 5.2. This will resolve
complaints about artificial requirement to keep build out of source folder
which produces clutter on disk when working with multiple Qt projects.

Task-number: QTCREATORBUG-10024
Change-Id: Ib05c78f4e8f55eb71e94d255f74543d31f2d569f
Reviewed-by: Daniel Teske <daniel.teske@digia.com>