Just asked a similar question — habrahabr.ru/qa/4370/
Opted for wxWigdets, by a number of significant reasons. By the way, the LGPL and the characteristics of the "old and reliable", "active project", etc. are also present.
Working draft 3rd day — flight normal, problems have not yet been found. Test compile behave predictably and all in all quite adequately.
On the Internet write about the problems with the documentation, but I have not found — there are a lot of Russian documentation to quickly find answers to your questions. Google knows everything.