Call the generator "Visual Studio 14" without any year because this
version of VS does not provide a year in the product name.
Copy cmGlobalVisualStudio12Generator to cmGlobalVisualStudio14Generator
and update version numbers accordingly. Add the VS14 enumeration value.
Teach the platform module Windows-MSVC to set MSVC14 and document the
variable. Teach module InstallRequiredSystemLibraries to look for the VS
14 runtime libraries.
Teach tests CheckCompilerRelatedVariables, VSExternalInclude, and
RunCMake.GeneratorToolset to treat VS 14 as they do VS 10, 11, and 12.
Co-Author: Pawel Stopinski <firstname.lastname@example.org>