Finally managed it to get a build with webengine. You have just to execute the "qmake -r WEBENGINE_CONFIG+=use_system_ffmpeg" BEFORE ".configure" then it works :-p
I`ve deployed the build over to development machine without problems.
There are now just two compiler errors left which I think can be solved:
libicu18n.so.55 not found (I think i can solve it by installing a icu18n-5 package if there are any?)
Undefined references to dbus: "dbus connection unref" and so on, much more errors referencing to dbus (this is actually coming from webengine)
How can I make a build which does not use libicu and dbus or at least uses system ones (if that helps in my case) ?