C89 conformance (old ANSI standard)

[SamuelMarks]

C89 is the most portable C implementation, even in 2021. Everything from FFI to compiler support is better on C89 than any newer standard. Conformance isn't difficult, but the first time around does require some brain-numbing reshuffling of code. I've done a portion of it, and will finish it (just @ tag me if you want it).