__cxa_demangle uses malloc/free for memory management, see
<http://itanium-cxx-abi.github.io/cxx-abi/abi.html#demangler>

Change-Id: I57f8465d1c70fbef4537068fd3aefc52295e1c63
Reviewed-on: https://gerrit.libreoffice.org/71942Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>