With the LLVM SVN code, support for being able to build the compiler infrastructure and library under Microsoft's Visual Studio 2008 C++ Compiler is no more. There's been a discussion about dropping support for older host compilers, in part so LLVM's code-base can begin to take use of modern C++11 features not supported by older code compilers.
Google's Chandler Carruth made the call yesterday after mixed discussions on the mailing list to drop VS 2008. Aside from the developers wanting to use modern C++ functionality, other reasons is not having enough contributors to support VS2008, focus should be given on supporting modern Microsoft platforms, and those stuck to using Visual Studio 2008 can remain using an older LLVM snapshot.
It's good to see though LLVM moving forward in wanting to leverage modern C++ code rather than supporting legacy compilers. They have been looking forward to modern C++ for improving code cleanliness, maintainability, simplicity, better performance, and other factors.
This change will be found in LLVM 3.4, which is likely to be released before year's end. Other changes include the AMD R600 GPU back-end is enabled by default, expanded use of the loop vectorizer, and performnace improvements.