Not all of them, and today is 2016, important C11 feature, like _Generic still not supported. And it would be awesome, if MSVC will support GNU extensions, like Clang does. For now I recommend to use clang-cl wrapper: http://clang.llvm.org/docs/MSVCCompatibility.html

For Visual C++ only to the extent as required by the C++ standard.

Clang/C2 is exactly the path for those that still care about C on Windows.