[BUG]: Link Error

Required prerequisites

• Make sure you've read the documentation. Your issue may be addressed there.
• Search the issue tracker and Discussions to verify that this hasn't already been reported. +1 or comment there if it has.
• Consider asking first in the Gitter chat room or in a Discussion.

Problem description

How to use my own link library in pybind11??

here is the example code:

test1.h
int add(int a, int b);

test1.cpp

int add(int a, int b){
    return a+b;
}

test2.cpp

#include "test1.h"
#include <pybind11/pybind11.h>
namespace py = pybind11;
int add2(int a, int b){
    return add(a, b)+add(a,b);
}
PYBIND11_MODULE(example, m) {
    m.doc() = "test extra link";
    m.def("add2", &add2, "A function which adds two numbers");
}

firstly, I make test1 to a link library. Then, I use setup.py to make the module.

setup.py

from pybind11.setup_helpers import Pybind11Extension, build_ext
import setuptools
library_dirs = ["./"]
def get_extensions():
    ext_modules = [Pybind11Extension('example', 
        ['test2.cpp'], 
        extra_compile_args=['-Xlinker','-export-dynamic'],
        extra_link_args = ['-L{} -ltest1'.format(library_dirs[0])],
        cxx_std=11),]
    return ext_modules

setuptools.setup(
    name='example',
    ext_modules=get_extensions(),
    cmdclass={'build_ext': build_ext},
    classifiers=["Programming Language :: Python :: 3", "Operating System :: OS Independent"],
    packages=setuptools.find_packages(),
)

here is the Error:

when I ldd the .so get this:

It seems that didn't link the test1.so

Reproducible example code

No response

Start with setup.py and the test1.cpp/test2.cpp example, then inspect the extension build and link command and compare it with the reported ldd output. Determine whether the issue indicates a pybind11 or build-helper problem and document the supported configuration or a reproducible correction; done means the example links and loads with its external library.