win32_io.c: use stat on Cygwin

Fixes compiler error (among others):

win32_io.c: In function 'ntfs_device_win32_stat':
win32_io.c:1804:31: error: invalid application of 'sizeof' to incomplete type 'struct stat64'
 1804 |         memset(buf, 0, sizeof(struct stat));
      |                               ^~~~~~

libntfs-3g/win32_io.c

@@ -61,7 +61,9 @@ typedef unsigned long long DWORD64;
 #endif
 #ifdef HAVE_SYS_STAT_H
 #include <sys/stat.h>
+#ifndef __CYGWIN__ /* See https://cygwin.com/faq.html#faq.programming.stat64 */
 #define stat stat64
+#endif
 #define st_blocks  st_rdev /* emulate st_blocks, missing in Windows */
 #endif