Use setmode() instead of _setmode()

Looks like Cygwin / MSVC declare it that way, and it still works on
MinGW32 cross.

util/options.hh

diff --git a/util/options.hh b/util/options.hh
index ad925b2..298a3f2 100644
--- a/util/options.hh
+++ b/util/options.hh
@@ -44,7 +44,7 @@
 #include <unistd.h> /* for isatty() */
 #endif
 #ifdef HAVE_IO_H
-#include <io.h> /* for _setmode() under Windows */
+#include <io.h> /* for setmode() under Windows */
 #endif
 
 #include <hb.h>