I spend several hours researching how to build a Qt app (written in C++) on Debian for users who will run it on Windows. I also wanted it be just one binary at the end so that deployment is just a matter of copying and running the one executable. This means I needed to statically-link the app, and the sad news is that I first needed a statically-linked Qt.
If I had actually known of M cross environment (MXE), I would have
shaved nearly all of those 'wasted' hours. I am very grateful to the
developers, especially because building Qt was mainly a matter of
installing a few build dependencies and running make qt. An hour or
two later, I had a newly cross-compiled Qt waiting for my use. It was
also pleasant that the app, in a form of a .exe file, just worked on
Windows 7.
Having a look around, the build system actually looks elegant, and is a lot simpler than the scary mess that is JHBuild.
I have published two guides on Stack Overflow on how this works, one for Qt 4 and another for Qt 5.