RFR: JDK-8139735: Switch compilers in JPRT for windows and linux

[Tim Bell]

Erik:

> The compilers used for building the product internally at Oracle is 
> changing soon for Windows and Linux. This change is needed to instruct 
> JPRT to use the new compilers.
>
> I also include updates to the devkit generating scripts for these 
> platforms.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8139735
> Webrev: http://cr.openjdk.java.net/~erikj/8139735/webrev.01/

Looks good.

Tim