You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: mkpost.go
    path of file: ./repos/xorm/vendor/golang.org/x/sys/unix
    
    the code of the file until where you have to start completion: // Copyright 2016 The Go Authors. All rights reser
    
func main() {
	b, err := ioutil.ReadAll(os.Stdin)
	if err != nil {
		log.Fatal(err)
	}
	s := string(b)

	goarch := os.Getenv("GOARCH")
	goos := os.Getenv("GOOS")
	if goarch == "s390x" && goos == "linux" {
		// Export the types of PtraceRegs fields.
		re := regexp.MustCompile("ptrace(Psw|Fpregs|Per)")
		s = re.ReplaceAllString(s, "Ptrace$1")

		// Replace padding fields inserted by cgo with blank identifiers.
		re = regexp.MustCompile("Pad_cgo[A-Za-z0-9_]*")
		s = re.ReplaceAllString(s, "_")

		// Replace other unwanted fields with blank identifiers.
		re = regexp.MustCompile("X_[A-Za-z0-9_]*")
		s = re.ReplaceAllString(s, "_")

		// Replace the control_regs union with a blank identifier for now.
		re = regexp.MustCompile("(Control_regs)\\s+\\[0\\]uint64")
		s = re.ReplaceAllString(s, "_ [0]uint64")
	}

	// gofmt
	b, err = format.Source([]byte(s))
	if err != nil {
		log.Fatal(err)
	}

	// Append this command to the header to show where the new file
	// came from.
	re := regexp.MustCompile("(cgo -godefs [a-zA-Z0-9_]+\\.go.*)")
	b = re.ReplaceAll(b, []byte("$1 | go run mkpost.go"))

	fmt.Printf("%s", b)
}