Is this a relatively recent MinGW installation - Aug 2013 or later? I ran into a compiler bug last fall that had me try updating my MinGW installation, and that was disastrous. IIRC the code wouldn't even compile, so atleast you are past that. Also IIRC it would crash immediately on startup when using the __argv/c. Changing to _argv/c worked, but MSVC hated that or something. In the end I managed to stick with my older installation using w32api3.x (it was w32api4.x that broke everything I think) and just updated the compiler.
I think Ters had done some further investigation, but I don't think any of the required changes made it into the Simutrans code. So I think the current state is if you want to use MinGW, you need an older installation.