[Development] gnuwin32 in qt5.git

[Frederik Gladhorn]

Hi all,

I'd like to have some opinions about the gnuwin32 we currently have in 
qt5.git. This way we provide flex and bison for Windows.
I think it's a bit mis-placed, in my opinion the tools which are needed on 
Windows should be in their own sub-module.

I think we should continue to ship them as dependencies and have them 
available easily for developers. But placing them directly in the qt5 
repository makes little sense. In Coin we have weird work around and more code 
that should be needed to make sure they are always in the right place.

Assuming there are no better ideas, I'll request a new repository soon.

Cheers,
Frederik