[3dprinter-general] Bug#950346: Bug#950346: please mark some more symbols as optional

[Gregor Riepl]

> please mark some more symbols as optional, seen when building with -O3 on
> ppc64el and s390x.
> 
> patch at
> http://launchpadlibrarian.net/462915998/libsavitar_4.4.1-1_4.4.1-1ubuntu1.diff.gz

These look good to me, please apply the patch.

I still don't get why so many STL symbols are exported with
-fvisibility=hidden. Seems like a gcc bug to me...