MinGW: Use our snprintf/vsnprintf when MinGW's is broken

All versions of MinGW-w64 prior to version 3, as well as
all versions of MinGW32 have broken implementations of
vsnprintf.

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>

compat/msvcrt/snprintf.c

@@ -27,6 +27,10 @@
 #include "compat/va_copy.h"
 #include "libavutil/error.h"
 
+#if defined(__MINGW32__)
+#define EOVERFLOW EFBIG
+#endif
+
 int avpriv_snprintf(char *s, size_t n, const char *fmt, ...)
 {
     va_list ap;