compiler: build separation runtime with clite

runtime/internal/lib/os/sys_unix.go

@@ -0,0 +1,14 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build unix
+
+package os
+
+// supportsCloseOnExec reports whether the platform supports the
+// O_CLOEXEC flag.
+// On Darwin, the O_CLOEXEC flag was introduced in OS X 10.7 (Darwin 11.0.0).
+// See https://support.apple.com/kb/HT1633.
+// On FreeBSD, the O_CLOEXEC flag was introduced in version 8.3.
+const supportsCloseOnExec = true