http://msdn.microsoft.com/en-us/library/hh162058.aspx
What's New in MSBuild 12.0 ? MSBuild is now installed as part of Visual Studio rather than as part of the .NET Framework. The current MSBuild version number is 12.0. If you want to install MSBuild separately, download the installation package from MSBuild Download.
http://www.microsoft.com/en-us/download/details.aspx?id=40760
I'm not a big fan of this (moving it from the framework install). But it is what it is.
But you have an issue now.
Supported Operating System : Windows 7 Service Pack 1, Windows 8, Windows 8.1, Windows Server 2008 R2 SP1, Windows Server 2012, Windows Server 2012 R2