..with libc++ on macOS:

> /Users/stephan/Software/lo2/core/sw/source/core/doc/CntntIdxStore.cxx:238:44: error: static_cast from 'decltype(__x.base() - __y.base())' (aka 'long') prvalue to 'long' prvalue is redundant [loplugin:redundantcast]
>                 const MarkEntry aEntry = { static_cast<long>(ppBkmk - pMarkAccess->getAllMarksBegin()), false, pBkmk->GetMarkPos().nContent.GetIndex() };
>                                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Change-Id: I94ab3d828482462c0fde26e19c9cc6508efa00fe
Reviewed-on: https://gerrit.libreoffice.org/59240
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>