The MSBuild version for each Visual Studio generator isn't 4.0. With
Visual Studo 2013 the ToolsVersion moved from being tied to the .NET
framework and now has its own version number.
Since we do not need the information about the target architecture
we can use the PlatformName only to specify the this information.
This also removes setting of the MSVC_*_ARCHITECTURE_ID variable
which is not required, because this variable gets set by the
compiler detection code in CMAKE_DETERMINE_COMPILER_ID_CHECK().
Copy cmGlobalVisualStudio11Generator to cmGlobalVisualStudio12Generator
and update version numbers accordingly. Add the VS12 enumeration value.
Add module CMakeVS12FindMake to find MSBuild. Look for MSBuild in its
now-dedicated Windows Registry entry. Teach the platform module
Windows-MSVC to set MSVC12 and document the variable. Teach module
InstallRequiredSystemLibraries to look for the VS 12 runtime libraries.
Teach tests CheckCompilerRelatedVariables, Preprocess, VSExternalInclude,
and RunCMake.GeneratorToolset to treat VS 12 as they do VS 10 and 11.
Inspired-by: Minmin Gong <minmin.gong@gmail.com>