RFR: 8246032: Implementation of JEP 347: Adopt C++14 Language Features in HotSpot

[Kim Barrett]

I just noticed that doc/building.{md,html} describes minimum toolchain versions,
so also needs to be updated.  Here’s the update, matching what’s now in the JEP:

full: https://cr.openjdk.java.net/~kbarrett/8246032/open.05/
incr: https://cr.openjdk.java.net/~kbarrett/8246032/open.05.inc/

I also deleted a discussion of a problem one might run into when building with
Visual Studio 2010, since that version is no longer relevant.