ntfsusermap.c: provide mode with mkdir

The desired mkdir does not seem to exist on Cygwin.

Fixes compiler error:

ntfsusermap.c: In function ‘outputmap’:
ntfsusermap.c:817:25: error: too few arguments to function ‘mkdir’
  817 |                         mkdir(fullname);
      |                         ^~~~~
In file included from /usr/include/sys/_default_fcntl.h:212,
                 from /usr/include/sys/fcntl.h:3,
                 from /usr/include/fcntl.h:13,
                 from ntfsusermap.c:113:
/usr/include/sys/stat.h:140:9: note: declared here
  140 | int     mkdir (const char *_path, mode_t __mode );
      |         ^~~~~

ntfsprogs/ntfsusermap.c

@@ -814,7 +814,12 @@ static boolean outputmap(const char *volume, const char *dir)
 			/* build directory, if not present */
 		if (stat(fullname,&st) && (errno == ENOENT)) {
 			printf("* Creating directory %s\n", fullname);
+			#ifdef __CYGWIN__
+			// The one-argument mkdir is exclusive to msvcrt.dll.
+			mkdir(fullname, 777);
+			#else
 			mkdir(fullname);
+			#endif
 		}
 
 		strcat(fullname, DIRSEP);