Fixed bug 3336 - Failure to build with MinGW-w64

Kai Sterker
There are already patches available from mingw64 that fix the issue

https://github.com/Alexpux/MINGW-packages/tree/master/mingw-w64-SDL2

With those applied, I could compile SDL2 without problems. But of course, it would be preferable if SDL built cleanly from source.

include/SDL_stdinc.h

@@ -93,6 +93,13 @@
 #define SDL_arraysize(array)    (sizeof(array)/sizeof(array[0]))
 #define SDL_TABLESIZE(table)    SDL_arraysize(table)
 
+/**
+ *  Macro useful for building other macros with strings in them
+ *
+ *  e.g. #define LOG_ERROR(X) OutputDebugString(SDL_STRINGIFY_ARG(__FUNCTION__) ": " X "\n")
+ */
+#define SDL_STRINGIFY_ARG(arg)  #arg
+
 /**
  *  \name Cast operators
  *