Cannot combine CGO on Mac OS - Undefined symbols for architecture x86_64

Getting Help Code Review
1

main.go

package main
/*
#cgo CFLAGS: -g -Wall
#include <stdlib.h>
#include "greeter.h"
*/
import "C"
import (
	"unsafe"
)

func main() {
	name := C.CString("Gopher")
	defer C.free(unsafe.Pointer(name))

	year := C.int(2018)

	C.greet(name, year)
}

greeter.h

#ifndef _GREETER_H
#define _GREETER_H

void greet(const char *name, int year);
#endif

greeter.c

#include "greeter.h"
#include <stdio.h>

void greet(const char *name, int year) {

    printf("Greetings, %s from %d! We come in peace :)", name, year);

}

cmd
$ go build -buildmode=c-archive -o greeter.a main.go

//output

# command-line-arguments
Undefined symbols for architecture x86_64:
  "_greet", referenced from:
      __cgo_4d6b7d3a5d3b_Cfunc_greet in _x002.o
     (maybe you meant: __cgo_4d6b7d3a5d3b_Cfunc_greet)
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Have you ever solve this, could you give me any advice?
Thanks,

2 
$ ls
greeter.c  greeter.h  main.go

$ go build -buildmode=c-archive -o greeter.a

$ ls
greeter.a  greeter.c  greeter.h  main.go
$