Document __FreeBSD_version 1100042 and 1100043

Differential Revision:	https://reviews.freebsd.org/D1110
Reviewed by:	bapt@, wblock@
Approved by:	bapt@, wblock@


git-svn-id: svn+ssh://svn.freebsd.org/doc/head@45926 c2e8774f-c49f-e111-b436-862b2bbc8956