RFR: JDK-8199266: Update boot and build jdk requirements in configure

[Magnus Ihse Bursie]

On 2018-03-07 22:24, Erik Joelsson wrote:
> When we bumped the feature version from 10 to 11, we forgot to also 
> update the required versions of the boot and build jdk. This is an 
> easy mistake to do, so we should make sure it is easy and intuitive to 
> do the update at the same time as updating the version number.
>
> This patch changes the check for build jdk to simply compare with the 
> current VERSION_FEATURE. This should always be the correct requirement.
>
> The check for boot jdk is a bit more complicated. I initially thought 
> we could calculate it automatically from VERSION_FEATURE-1, but until 
> that version is actually released, we need to also allow 
> VERSION_FEATURE-2. Because of this we will still require manual 
> updating of this setting over time. So instead I moved the set of 
> acceptable boot JDK versions to the version_numbers file. This should 
> make it easy enough to spot and update when changing the 
> DEFAULT_VERSION_FEATURE value.
>
> I also updated the build documentation regarding boot JDKs to explain 
> temporary N-2 situation. While at it, I also updated the part about 
> where to get JDK binaries since you can now download OpenJDK builds 
> directly from jdk.java.net.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8199266
>
> Webrev: http://cr.openjdk.java.net/~erikj/8199266/webrev.01/
Looks good to me.

/Magnus

>
> /Erik
>