"export" the qml tools for qtPrepareTool() use

"export" the qml tools for qtPrepareTool() use

notably, this disables the build of qmlplugindumpd.exe under windows -
it is not clear to me why somebody would want to do that, as both sets
of libraries would be available, and the output from both variants should
be the same.

Change-Id: I95c77b2aa32f17f9d6df0e5d4b9d11f456d860f6
Reviewed-by: Rohan McGovern <rohan.mcgovern@nokia.com>