RFR: JDK-8205183: Warning about using VS2017 should be removed

Mon Jun 18 20:34:24 UTC 2018

When using VS2017, configure prints a warning about the toolchain being 
unsupported. This needs to change now that this is the main toolchain 
version for OpenJDK on Windows (at least for Oracle).

This patch removes the warning for VS2017 and adds it back for all other 
versions of Visual Studio. I've made it possible to toggle this 
individually for each VS version so if someone wants to claim support 
for another VS version, they can flip it back.

Bug: https://bugs.openjdk.java.net/browse/JDK-8205183

Webrev: http://cr.openjdk.java.net/~erikj/8205183/webrev.01/

/Erik