qt4 vs qt5 build for dependencies

[Stephen Kelly]

Stephen Kelly wrote:

> Alexander Neundorf wrote:
>> Is there a plan what to do with Qt5Transitional.cmake from e-c-m ?
> 
> When qt5.git is updated, we can try to remove the use of it.
> 

I've done that now.

In the process I used more imported target names for using Qt. 

I you don't like that, so if you change them all to use variables instead, I 
won't make a fuss (but I also won't see the point).

Thanks,

Steve.