Bug#931921: clutter's autopkgtests hang when ran with a libglib2.0-0 built with gcc-9

[Simon McVittie <smcv@debian.org>]

On Fri, 12 Jul 2019 at 11:16:53 +0100, Iain Lane wrote:
> I saw this on Ubuntu (9.1.0-8ubuntu1) but I've also reproduced this with
> 9.1.0-8 on sid (w/gcc-defaults from experimental to use gcc-9 by
> default).
> 
> clutter's tests hang:
...
> It's adding some stuff to a main loop and expecting it to finish when a
> particular signal handler is called.

I can reproduce this with current unstable GLib, 2.60.6-1 (after reverting
the change that makes it explicitly build with gcc 8).

In the non-working case, it looks as though the paint signal is not
getting emitted at all. The Clutter master clock appears to be the thing
that is meant to be scheduling GLib main-loop events in this case (and
then I got lost and couldn't work out what was wrong).

> Things which make it work again
> 
>   - Building glib2.0 w/gcc-9 -O1 (and -O0)
>   - Building w/gcc-8 (obviously)

I can confirm that a GLib built from the same source code with gcc-9 -O1
works fine.

I have been trying to reproduce this with the upstream GLib source code
so that I can try a build of GLib with ThreadSanitizer or AddressSanitizer,
but so far this has not been successful.

    smcv