The mingw toolchain is for cross compiling to target Windows. It is very mature and are used by many open source projects, especially desktop software which is popular on Windows but mostly developed by people running Linux.
In many cases you wouldn't even need cross compilation if you can run Windows tools directly on WINE. Years ago I installed Delphi 6 on a Linux machine with WINE, and although I didn't write any complex stuff or imported 3rd party components, it compiled every Delphi code I threw at it, producing native Windows code that ran flawlessly on Windows machines.
We actually run MSVC builds for Linux by running the VC++ toolchain in Wine, it works very well apart from process startup times, which have been getting a lot better.
