$FreeBSD: head/lib/libopenbsd/README 290378 2015-11-05 01:54:38Z rodrigc $

libopenbsd is a thin compatibility layer intended to allow a limited
set of OpenBSD software to compile as part of the FreeBSD build with
little or no modification.  It is built as a static library and not
installed for general use.  Likewise, its header files are not
installed.