[1] http://blogs.msdn.com/b/vcblog/archive/2013/07/19/c99-librar...
It does not actually allow you to write compliant C99 and compile it.
https://channel9.msdn.com/Events/Visual-Studio/Launch-2013/V...
A would like to see a similar article for OpenWatcom v2.
C++ is now supported on the kernel level.
Good luck doing WinRT applications with pure C.