WinRT: Fix Widget builds

Tweak pri files and preprocessor usage to support widgets under WinRT.

Change-Id: I6dc7d160078c0da343d6d39d2a0d52112c6f9f59
Reviewed-by: Andrew Knight <andrew.knight@digia.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>