editors/openoffice-devel: make robust against __cxa_exception ABI changes

Patch openoffice to replace cxa_get_globals()->caughtExceptions,
which is a pointer to the start of a struct cxa_exception, with
cxa_current_primary_exception(), which is a pointer to the end. This
allows struct cxa_exception to be extended at the start as was
recently done in FreeBSD main and stable/13 on 64-bit architectures.

Recently on FreeBSD main and stable/13 attribute((aligned)) was
added to struct _Unwind_Exception which changes its size on 32-bit
architectures, and that of __cxa_exception as well. Patch openoffice
to detect this so packages built on 13.0 still work on 13.1.

Add a build dependency on a recent version of devel/libunwind so we
always build with an unwind.h that has the right definition of
_Unwind_Exception. The dependency was already pulled in via gstreamer
(with default options).