updated for version 7.3.177
Problem:    MS-Windows: mkdir() doesn't work properly when 'encoding' is
            "utf-8".
Solution:   Convert to utf-16. (Yukihiro Nakadaira)
diff --git a/src/os_win32.h b/src/os_win32.h
index 527d8c7..41a44bf 100644
--- a/src/os_win32.h
+++ b/src/os_win32.h
@@ -191,5 +191,5 @@
 #ifdef __BORLANDC__
 # define vim_mkdir(x, y) mkdir(x)
 #else
-# define vim_mkdir(x, y) _mkdir(x)
+# define vim_mkdir(x, y) mch_mkdir(x)
 #endif