Bug#795288: nmu: libsigc++-2.0_2.4.1-2

[Edmund Grimley Evans <edmund.grimley.evans@gmail.com>]

> Could you outline why you believe a binNMU would fix the issue please?

On arm64, libsigc++-2.0_2.4.1-2 (and thus libsigc++-2.0-0v5) was built
with g++-4.9, although it was built on Aug 6, after build-essential_12
was installed. This happened because arm-arm-03 failed to regenerate
its chroot on Aug 2. This is likely to cause problems...

The Aug 2 build log for synfigstudio has this error:

synfig -q layer_filter_clamp_icon.sif -o layer_filter_clamp_icon.png --time 0
*** Error in `synfig': munmap_chunk(): invalid pointer: 0x0000000014e27940 ***

The error is easy to reproduce: the synfig command (from the synfig
package) is failing. The stack trace (if you run it under gdb) mentions the
C++ types that are typically problematic with the GCC 5 transition.

When I rebuilt libsigc++-2.0, the problem went away.

There's now another synfigstudio build log with a different error, but the
same synfig command is involved, so the cause is probably the same.

(There are other, similar problems caused by C++ libraries having been
built for arm64 by arm-arm-03 with g++-4.9 in the period Aug 3-9. I expect
this will haunt us for a while.)

Thanks,

Edmund