unix: file: No fsync() on Windows.

unix/file.c

@@ -83,8 +83,12 @@ STATIC mp_int_t fdfile_write(mp_obj_t o_in, const void *buf, mp_uint_t size, int
 }
 
 STATIC mp_obj_t fdfile_flush(mp_obj_t self_in) {
+#ifndef _WIN32
     mp_obj_fdfile_t *self = self_in;
     fsync(self->fd);
+#else
+    //TODO
+#endif
     return mp_const_none;
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(fdfile_flush_obj, fdfile_flush);