With Redtamarin (based on AVM2), there is a native library which sole purpose is to give direct access to C and other syscalls.

For ex with getaddrinfo: https://gist.github.com/zwetan/0c047d36542cc6979652

I know because I did it on purpose, even if it managed code written in AS3 you don't want to reinvent getaddrinfo, you want to reuse it "as is" as much as possible.