Invokes gdb, which attaches to the current process and shows a stack trace.
This function may cause different actions on non-UNIX platforms.
When running on Windows, this function is *not* called by on_error_query. If called directly, it will raise an exception, which will crash the program. If the `G_DEBUGGER` environment variable is set, a debugger will be invoked to attach and handle that exception (see [Running GLib Applications](glib-running.html)).
the program name, needed by gdb for the "[S]tack trace" option