RFR: JDK-8076531: Switch default compiler on Windows to VS2013

[Erik Joelsson]

Hello,

Please review this change which will make the official switch of the 
preferred compiler toolchain on Windows for JDK 9.

Changes are needed in:

* configure, for changing the default when multiple versions are available
* jprt.properties, for picking the right type of machine for Oracle 
internal building
* README-builds.html to make the documentation a little more correct in 
reflecting the current state of the build requirements

Note that README-builds certainly needs a lot more love, but this is not 
the time for correcting the rest of the mess. I'm only updating the 
numbers so that it's no longer blatantly wrong.

Bug: https://bugs.openjdk.java.net/browse/JDK-8076531
Webrev: http://cr.openjdk.java.net/~erikj/8076531/webrev.01/

/Erik