Hello Bogdan,

>   Can you tell us what actually "c++" is on your system? Like e.g. run
> "c++ --version" or "c++ --help"?

$ c++ --version
OpenBSD clang version 13.0.0
Target: amd64-unknown-openbsd7.4
Thread model: posix
InstalledDir: /usr/bin

>   On my system, Autoconf finds "g++", tests it for an Objective C++
> compiler, fails, and the t/objcxx-* tests are simply skipped.
>   It seems that on your system, "c++" actually works as an Objective
> C++ compiler, but somehow the "libobjc" library is not added to the
> command line, making the test fail during linking.

Yes, 'c++' works as an Objective-C++ compiler:
================================= hello.mm ==========================
#import <stdio.h>
#import <stdlib.h>
#import <iostream>

class X { int a; };

int main(void)
{
    @autoreleasepool
    {
        std::cout << @"Hello, Objective-C++.";
    }
    
    return EXIT_SUCCESS;
}
======================================================================
$ c++ -c hello.mm
$ c++ hello.mm
[3 link errors, due to undefined symbols.]

>   What Autoconf version do your have and can you upgrade that?

I was testing automake-1.16j.

> I suspect it's not passing the required libraries. If it's the newest
> version, can you attach the config.log file?

Find attached the config.log.

Bruno