qt4 vs qt5 build for dependencies

[Stephen Kelly]

David Faure wrote:
> Later on, when we're about to release KF5, we want to turn this around,
> i.e. make it easy to build things for Qt5, and if we still need qt4
> support at that point, adding a -DQT4_BUILD=true (and dropping the
> QT5_BUILD variable, obviously).

I'd say skip adding the QT5_BUILD variable, and just add QT4_BUILD now.

Thanks,

Steve.