git: openjdk/jdk: 8251210: Link JDK api docs to other versions

[Jonathan Gibbons]

Changeset: b1cc864a
Author:    Jonathan Gibbons <jjg at openjdk.org>
Date:      2021-03-08 16:19:48 +0000
URL:       https://git.openjdk.java.net/jdk/commit/b1cc864a

8251210: Link JDK api docs to other versions

Reviewed-by: iris, erikj

! make/Docs.gmk
! make/conf/javadoc.conf