Why not CMake for gns-sys build?

[debroejm]

For context, I'm working on a pull request to fix building for Windows, since building gns-sys for Windows is just completely broken. (missing some Windows-specific .c files from upstream, wrong names for libs, etc).

Looking at upstream, GNS uses CMake for its build process. While I haven't delved into trying to use it yet, it appears there is a Rust build dependency for CMake, and I'm curious if there are any reasons that the current cc build dependency is used instead? Manually specifying the build process in build.rs makes it extremely easy to get out of sync, as seen by the above issues with building for Windows. Even worse, upstream already has the appropriate configuration to deal with different platform building, so fixing Windows builds in gns-sys would be duplicating some of that per-platform logic.

tl;dr: Any reason that upstream GNS is compiled with cc in gns-sys, and not CMake? If not, is it alright if I go ahead and make a pull request to switch to CMake?