The build on FreeBSD wasn't *quite* working.
A few surprisingly minor fixes to support building 389ds on FreeBSD:
* slapd: Don't use `O_PATH' if it's not available.
* slapd: Don't invoke `#include' inside a function.
* slapd: Move the `#include' of libgen.h to grab basename(3).
* pwdstorage: Set `_BSD_SOURCE'; and fix up includes for FreeBSD.
* slapd: statvfs(3) doesn't have `f_mntonname', but statfs(2) does.
* libaccess: `LASIpAddPatternIPV6' returns `int'; `NULL' can't be cast.
* buildnum.py: Use `env' to find python3.
* autogen: Use `gsed' (hopefully GNU sed) if it's available.
Author: Jashank Jeremy (@jashankj)
Review by: William Brown (@firstyear)