win64: use new headers from mingw

win32/include/stdarg.h

@@ -1,19 +0,0 @@
-#ifndef _STDARG_H
-#define _STDARG_H
-
-#ifndef _VA_LIST
-#define _VA_LIST
-typedef char *va_list;
-#endif
-
-/* only correct for i386 */
-#define va_start(ap,last) ap = ((char *)&(last)) + ((sizeof(last)+3)&~3)
-#define va_arg(ap,type) (ap += (sizeof(type)+3)&~3, *(type *)(ap - ((sizeof(type)+3)&~3)))
-#define va_copy(dest, src) (dest) = (src)
-#define va_end(ap)
-
-/* fix a buggy dependency on GCC in libio.h */
-typedef va_list __gnuc_va_list;
-#define _VA_LIST_DEFINED
-
-#endif