Fix windows build

[Khitiara]

Fixes #3
based on the contents of msvc.h

[Khitiara]

marked as draft until i make sure everything is working

[wozniak]

Hi, just bumping this. It seems like Windows does have mempcpy, or at least the headers that come with zig do now. I would very much like to see this merged, would be good a good step for the ffmpeg package that also currently does not work on Windows.

[Khitiara]

@wozniak this is currently marked as draft as afaik it doesnt actually work - last i checked it compiles successfully but the resultant binary crashes immediately without message