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

[Erik Joelsson]

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/

/Erik