Add a feature gate to call DebugBreak on construction

[AqlaSolutions]

trafficstars

On Windows, when appropriate feature is enabled, it would be cool to be able to run this kind of code when constructing a Error struct:

    if (unsafe { winapi::um::debugapi::IsDebuggerPresent() != 0 })
    {
         unsafe { winapi::um::debugapi::DebugBreak(); }
    }

It would cause the debugger, if attached, to break at the time of error construction so it's possible to see the stack locals and even interact with things.