A lot of the C99 features like array initialization got sucked into C++11, and since the C "compiler" in MSVC is the C++ compiler, I think you'll probably get most of C99 for free.
If only that were true - however, some of the more interesting C99 and C11 features aren't part of C++11 as there are already C++ specific alternatives.
Also, MS doesn't really have a good track record of backporting C++ features to C (mixing code and declarations, anyone?).
If you want to write portable C code that works on at least *nix and Windows, either ignore MSVC (GCC works just fine on Windows via MinGW or Cygwin cross-compiler, as does Clang once you get it set up), or restrict yourself to the common subset of C99 and C++98...