MacOS gcc dylib and clang app - exception handling issue - c++

Question

For a legacy project I have to compile our code into a dylib with gcc which is then linked into a clang app starting with Intel-based macOS 10.15 (Catalina). I work with Big Sur 11.4 on a Mac Mini 2020 M1.
For testing purposes, I have created a small C++ project with header
foo.h
#pragma once
class Foo
{
public:
Foo();
virtual ~Foo();
void throw_runtime_error(const char* msg);
int bar(int a);
};
and code foo.cpp
#include <iostream>
#include <stdexcept>
#include "foo.h"
using namespace std;
Foo::Foo()
{
cout << "Foo:Foo() called" << endl;
}
Foo::~Foo()
{
cout << "Foo:~Foo() called" << endl;
}
void Foo::throw_runtime_error(const char* msg)
{
cout << "throwing runtime_error " << msg << endl;
throw runtime_error( msg );
}
int Foo::bar(int a)
{
cout << "Foo::bar(" << a << ") called" << endl;
return a + 1;
}
To create the dylib in a build subdir, I use the homebrewn g++ 10.2 with
g++-10 -arch x86_64 -fexceptions -dynamiclib -I../include ../src/foo.cpp -o ../bin/libMyDylib.dylib
For testing, how to be used along with clang 12.2.0 I have created a main.cpp in the bin subdir
#include "../include/foo.h"
#include <iostream>
#include <stdexcept>
int main()
{
Foo foo;
try
{
foo.throw_runtime_error("Hello you ugly little creatures!");
}
catch( const std::runtime_error &r )
{
std::cout << "Caught foo runtime_error, what = " << r.what() << std::endl;
}
catch( const std::exception &x )
{
std::cout << "Caught foo exception, what = " << x.what() << std::endl;
}
catch(...)
{
std::cout << "Caught foo exception, but without what()" << std::endl;
}
return foo.bar(42);
}
Now, if I use gcc-10 to compile main.cpp and link it with libMyDylib.dylib via g++-10 -arch x86_64 -L/Users/macos/bin -lMyDylib main.cpp -o main the exception handler in main.cpp catches the std::runtime_error properly.
If I use clang 12.2 along with g++ -arch x86_64 -L/Users/macos/bin -lMyDylib main.cpp -o main
then the output shows that only the catch (...) handler is triggered.
./main
Foo:Foo() called
throwing runtime_error Hello you ugly little creatures!
Caught foo exception, but without what()
Foo::bar(42) called
Foo:~Foo() called
So, can someone please give me a hint, what I am missing, in order to get 'cross-compiler' exceptions properly handled?
Thnxalot