Nim memory debugging, trying dynamic lib, but it fails to compile on macOS

clib.nim

import strformat
import strutils
import sequtils

echo "clib initialized"
echo GC_getStatistics()

proc hello_echo*(message:cstring):cstring {.exportc.} =
  ## Echo a message back
  var s_message:string = $message
  result = &"{s_message} echo"
  # echo &"Nim echo result: {result}"
  
proc stats*() {.exportc.} =
  echo GC_getStatistics()

go.sh

#!/bin/bash

set -e
rm -r csrc || echo
mkdir -p csrc
cp ~/lib/Nim/lib/nimbase.h csrc/
nim c -f -o:libclib.dylib --app:lib --header --nimcache:csrc clib.nim
clang++ -o test test.cpp -lclib -L.
./test

output

$ ./go.sh 
Hint: used config file '/Users/matt/lib/Nim/config/nim.cfg' [Conf]
Hint: used config file '/Users/matt/lib/Nim/config/config.nims' [Conf]
Hint: system [Processing]
Hint: clib [Processing]
Hint: strformat [Processing]
Hint: macros [Processing]
Hint: parseutils [Processing]
Hint: unicode [Processing]
Hint: strutils [Processing]
Hint: math [Processing]
Hint: bitops [Processing]
Hint: algorithm [Processing]
Hint: sequtils [Processing]
CC: stdlib_system
CC: clib
Hint:  [Link]
Hint: operation successful (30080 lines compiled; 0.661 sec total; 38.414MiB peakmem; Debug Build) [SuccessX]
Undefined symbols for architecture x86_64:
  "hello_echo(char*)", referenced from:
      echo(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >) in test-ca3c9a.o
  "stats()", referenced from:
      _main in test-ca3c9a.o
  "NimMain()", referenced from:
      _main in test-ca3c9a.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

test.cpp

#include <iostream>
#include "csrc/clib.h"
using namespace std;

N_CDECL(void, NimMain)(void);

std::string echo(std::string arg) {
    const char* message = arg.c_str();
    cout << "C++ passing message: " << message << "\n";
    cout << "C++ message addr: " << (void*)message << "\n";
    char* retval = hello_echo(
        (char *)(message)
    );
    cout << "C++ retval addr : " << (void*)retval << "\n";
    return std::string(retval);
}

int main(void) {
    NimMain();
    cout << "Hello world\n";
    int i = 0;
    for (i = 0; i < 10000; i++) {
        std::string msg = "Hello " + std::string(i, '-');
        std::string ret = echo(msg);
        cout << "Got reply: " << ret << "\n";
    }
    stats();
    return 0;
}