MinGW-w64 use ANSI STDIO

Took me a while to get it done, but here's a change to fix issue #315.  I wasn't able to put the #define in PlatformSpecific.cpp since the forced includes for the new macros ends up pulling in stdio.h eventually (the include tree for that was a pain to chase).  I can try to find some #ifdef's to wrap around the #define if you want, but it seemed like that shouldn't really be necessary since the #define is pretty specific to just enabling a behavior that we pretty much always want on anyways.