The link you have posted is o.k ( although it is the 5.2 bugfix branch of the source code repository and not a release ). Follow it and you see a couple of filenames - one of this is named qwtconfig.pri. So if you don't have it and if you don't know what subversion is - where did you get your package from ?

If you want to find the Qwt project page and all official releases google for Qwt and you have it in 5 seconds.

Uwe