Re: RFR: JDK-8222735: Update doc/building.md with current Oracle build platforms and compilers

[Tim Bell]

Erik:

When updating the compilers used at Oracle earlier this year, I forgot
to keep building.md up to date. This needs to be fixed.

Bug: https://bugs.openjdk.java.net/browse/JDK-8222735

Webrev: http://cr.openjdk.java.net/~erikj/8222735/webrev.01/

Looks good.

Tim