Since VS2013 some useful and popular C99 language features are supported. And then there's Clang/C2 but it can't be used via command-line yet.

Their standard library (besides being intentionally not fully compliant) is missing some C11 features though. I guess we have to wait at least for C++17:

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p006...

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.

This is both C and C++ - they share a common backend (c2.dll) where this work was done. They have different front ends (c1.dll / c1xx.dll).