Decide what to do with references to the CRT

[retep998]

Occasionally some stuff in Windows API does reference the C standard library. In particular time_t and size_t are notable examples that have come up before. A decision needs to be made on how to deal with this.

[docbrown]

Can libc be added as a dependency?

[retep998]

What I'll probably do is put the Universal CRT stuff in the ucrt module and the VC++ headers (all the runtime bits) in the vc module. I'd rather not depend on libc if I can help it, especially because the CRT on Windows is implemented using Windows API. Also because I'm greedy and don't want to share winapi's downloads with other crates.

The real question is how to deal with different CRT versions. MinGW in particular uses a wildly different version with completely different runtime bits, and even VC++ has some changes over the years (switching to the Universal CRT being the most notable).