vlib: use new filename format

vlib/os/os_darwin.c.v

@@ -0,0 +1,18 @@
+// Copyright (c) 2019-2020 Alexander Medvednikov. All rights reserved.
+// Use of this source code is governed by an MIT license
+// that can be found in the LICENSE file.
+
+module os
+
+pub const (
+	sys_write = 4
+	sys_open = 5
+	sys_close = 6
+	sys_mkdir = 136
+	sys_creat =  8
+	sys_open_nocancel = 398
+	sys_stat64  = 338
+)
+
+
+