The tools like `adig` and `ahost` can take advantage of some of the
library functions within c-ares. We can't really split these library
functions into a helper library without possibly breaking users.
Technically if we could guarantee they rely on pkg-config or cmake
helpers we could make it work ... we can revisit that in the future,
maybe if we make a c-ares 2.0 where people might expect more breakage
(but I still wouldn't want to break API/ABI).

So what this does is it just exports some symbols in headers that aren't
distributed so end users aren't meant to use the symbols, but any
utilities or tests built by c-ares can. It does clutter up some of the
namespace, but all these symbols are guaranteed to be prefixed with
`ares_` so there shouldn't ever be symbol clashes due to this for end
users and its not so many symbols that it should affect any load times.

There will be **zero** API/ABI guarantees for these symbols. They can
change from release to release, this is ok since they are not public.

I'm not entirely thrilled with doing this solution, but I want to avoid
thing like hand-written parsers, such as is used in #856.

Authored-By: Brad House <(@bradh352)>