Undefined symbol "boost::this_thread::interruption_point()"

[clankill3r]

I'm using this library:
https://docs.websocketpp.org/faq.html

All the examples will build except one (https://github.com/zaphoyd/websocketpp/tree/master/examples/sip_client).
The one that does not build has one line it fails on which is the following line:

boost::this_thread::sleep(boost::posix_time::milliseconds(100));

Which gives the following error:

Undefined symbols for architecture x86_64:
  "boost::this_thread::interruption_point()", referenced from:
      boost::condition_variable::wait(boost::unique_lock<boost::mutex>&) in sip_client.cpp.o
      boost::condition_variable::do_wait_until(boost::unique_lock<boost::mutex>&, boost::detail::real_platform_timepoint const&) in sip_client.cpp.o
  "boost::detail::get_current_thread_data()", referenced from:
      boost::detail::interruption_checker::interruption_checker(_opaque_pthread_mutex_t*, _opaque_pthread_cond_t*) in sip_client.cpp.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[2]: *** [bin/sip_client] Error 1
make[1]: *** [examples/sip_client/CMakeFiles/sip_client.dir/all] Error 2
make: *** [all] Error 2

I tried it with boost 1_39_0, 1_46_1 and 1_80_0.

I'm on OSX 10.15.7. Let me know if I can help in any way.