Gilles Khouzam authored Sep 30, 2015 and Brad King committed Oct 02, 2015

Teach the VS 2015 generator to produce a WindowsTargetPlatformVersion
value.  Use the CMAKE_SYSTEM_VERSION to specify the version and if not
set choose a default based on available SDKs.  Activate this behavior
when targeting Windows 10.

Co-Author: Brad King <brad.king@kitware.com>