[8u] RFR: 8196108: Add build support for VS 2015/2017

[Kevin Walls]

Hi,

I'd like to get a review of a backport to jdk8u of:

8196108: Add build support for VS 2015/2017
https://bugs.openjdk.java.net/browse/JDK-8196108

JDK 11 changeset: http://hg.openjdk.java.net/jdk/jdk/rev/bcce1fa183e7

Original review thread: 
http://mail.openjdk.java.net/pipermail/build-dev/2018-January/020719.html

jdk8u webrev: http://cr.openjdk.java.net/~kevinw/8196108/webrev.00/

Imports partly automatically, partly needs manual intervention.

I haven't included the devkit creation scripts.  They aren't in 8 
already, we haven't backported: 8087208: Add devkit creation script for 
windows
The scripts are available in the later repos, and the devkits created 
are the same...  So it appears unnecessary.  I can start a build using 
VS2017 installed, or from a devkit.

Testing locally and with JPRT, using the existing default VS2010 
compiler, so the standard build is unaffected.

This change is not in 10 or 9, but this is a backport to 8.

This of course does not change anything about what compilers are known 
to work or be supported to build jdk8u, and in toolchain_windows.m4, for 
the ordering of compiler versions I kept VALID_VS_VERSIONS starting with 
2010, so no change in the default compiler we use.  Will be further 
changes to get the VS2017 build actually working...

Many thanks
Kevin