I know why you asked. That was quite obvious from your question and from the errors observed when attempting to build that C code. I've also assumed you've already run various Google searches and have come up empty, too.
It's obviously your decision to implement a new application using this particular design. You'll be among the few folks that are pursuing this particular challenge.
Most folks here will look to use libwww or one of the other available user interface frameworks, and are looking to migrate away from serial connections and away from (save for comparatively advanced tasks) character cell UIs. Which is almost certainly why you've also not located much in the way of free menu tools for OpenVMS, too.
FWIW, you'll probably be able to mask a number of the errors here using /STANDARD=VAXC on your C builds. Standard warning: that masks the errors, and doesn't fix the errors.
