Fix more problem with mingw this time

source/blender/blenlib/BLI_winstuff.h

@@ -91,11 +91,14 @@ extern "C" {
 typedef unsigned int mode_t;
 #endif
 
+#ifndef _SSIZE_T_
+#define _SSIZE_T_
 #if defined(_WIN64)
 typedef __int64 ssize_t;
 #else
 typedef _W64 int ssize_t;
 #endif
+#endif
 
 struct dirent {
 	int d_ino;