fileutils: fix definition of mode_t on windows

Change-Id: I19a93497aada7b89fe85bfac56ff6b896261e09c

include/fileutils.h

@@ -26,6 +26,8 @@
 
 #ifndef _WIN32
 #include <sys/stat.h>               // mode_t
+#else
+#define mode_t                unsigned
 #endif
 
 namespace dhtnet {