The getdtablecount.c file won't compile on Linux but it seems like none of
the bootstrap tools actually need it.
Reviewed By: emaste, brooks
Differential Revision: https://reviews.freebsd.org/D14244
libopenbsd is an internal library which
to bring in compatibility stuff from OpenBSD.
This will allow us to bring in more
OpenBSD utilities into the FreeBSD base system.
We similarly use libnetbsd for bringing in stuff from NetBSD.
Reviewed by: bapt
Differential Revision: https://reviews.freebsd.org/D4078