I have built Qt 5.8 from source on Windows successfully using the following configure line:
configure -prefix c:\qt\5.8\msvc2015_5_8_static_32 -commercial -debug-and-release -static -static-runtime -nomake examples -nomake tools -nomake tests -opengl dynamic -skip multimedia -skip qt3d -skip qtsensors -skip webengine
After a successful build QtCreator fails to recognize it. See screenshot.
However, I can use it normally through the command line.
I have posted this issue to the interest list and Thiago Macieira commented the following: "My guess is that this change to the way we store mkspecs in Qt 5.8 broke the detection on Qt Creator."