libevent: Import libevent 2.1.12MFC after: 2 weeksMerge commit '5223d1d95fddcef6f9a36e264a5800bd907ade8b' into main
libevent: eliminate in-tree usage of arc4random_addrandomApply r338059 to newly-added libevent 2.1.18.Approved by: re (gjb)Sponsored by: The FreeBSD Foundation
Copy libevent sources to contribTo replace the libevent embedded in ntp, for OpenSSL 1.1.1 compat.Approved by: re (gjb)