...with the added benefit of the implementation-provided versions being trivial
and so avoiding GCC 8 -Werror=class-memaccess when these classes are subject of
memcpy/memmove in store/source/stortree.cxx and store/source/storpage.cxx.

Change-Id: I684109d8743eb7f1fa57c6925d738b11d934a7cf
Reviewed-on: https://gerrit.libreoffice.org/40977Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>