RFR: Update build documentation to reflect compiler upgrades at Oracle

[Tim Bell]

Erik:

> The build documentation needs to be updated to reflect the compiler
> updates that took place at Oracle for JDK 11.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8208096
>
> Webrev: http://cr.openjdk.java.net/~erikj/8208096/webrev.01/

Looks good.

/Tim