http://blogs.msdn.com/b/vcblog/archive/2015/12/04/introducing-clang-with-micr...
To make it easier to develop cross-platform code that works well for both Windows and other platforms, we’ve released an additional compiler toolset for Visual Studio called Clang with Microsoft CodeGen. This compiler uses the open-source Clang parser for C and C++, along with the code generator and optimizer from the Visual C++ compiler. This lets you compile your cross-platform code for Windows using the same Clang parser that you use for other targets, while still taking advantage of the advanced optimizations from the Visual C++ optimizer when you build for Windows. Because the new toolset uses the same Clang parser used for non-Windows targets, you won't need to have annoying #ifdefs throughout the code just to account for differences between the compilers. Also, your code can take advantage of language features that are not currently available in the Visual C++ compiler, including C99 complex types and C++14 extended constexpr support. And because the Clang-based compiler generates the same debug information format as the Visual C++ compiler, you'll still be able to debug your code with the same great Visual Studio debugger experience.
Для неосиливших английский: МС добавили в visual studio 2015 update 1 возможность использовать шланг в качестве парсера, а в качестве бэкэнда микрософтовский коде-генератор, тем самым облегчив возможность писать кросс-платформенные приложения.
На мой взгляд это выглядит как признание того факта, что они не могут в полной мере реализовать c++11/c++14 (мы же знаем, как у них поддержка сильно хромала). Ну и решили не тратить ресурсы, когда шланг и так есть.
