[Issue 21919] darwin: SEGV in core.thread tests on OSX 11

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21919

--- Comment #5 from Iain Buclaw <ibuclaw at gdcproject.org> ---
To describe what looks like is happening:

1. A D fiber context switch occurs.
2. An exception is thrown.
3. libunwind's entry point for raising exceptions is called.
4. Segfault somewhere deep in libc/pthread.

The unittest block that matches the encoded line numbers in the function name
is:
---
// Test exception handling inside fibers.
unittest
{
    enum MSG = "Test message.";
    string caughtMsg;
    (new Fiber({
        try
        {
            throw new Exception(MSG);
        }
        catch (Exception e)
        {
            caughtMsg = e.msg;
        }
    })).call();
    assert(caughtMsg == MSG);
}

--