this is deprecated and have been long replaced by the mingw-w64 packages.
For the longest time I used Mingw + cmake on top of wine to cross compile my Qt4 apps for windows, then I was bored one day, tired of how slow it is to recompile qt4 on wine and decided to try to get it to work with a native gcc instead of the overhead with wine.
So here goes.
This was done on Gentoo Linux, please don't ask me how to do it on other distros.
1. You know your way around the linux shell and have portage privileges.
2. You're not scared from compiling things by hand.
3. You already have Qt4 installed and it is the same version as the windows source we gonna build.
4. Your working path will be ~/win32.
5. You have a working wine setup.