I made my changes compatible with older versions of Boost by using Boost's digest_type instead of hard-coding the underlying type we expect Boost to use.

It looks like this PR may need to be rebased onto the current master, since I'm seeing changes here that were merged in by another PR.

@afh Does this PR look good to you now?

I'm doing test builds with boost 1.86 and a previous version, while having a closer look at the changes this very moment :)

While this PR builds with a previous version of boost, it unfortunately fails when building with boost 1.86.0 with:

src/utils.h:602:18: error: non-const lvalue reference to type 'digest_type' (aka 'unsigned char[20]') cannot bind to a value of unrelated type 'unsigned int[5]'
    sha.get_digest(message_digest);
                   ^~~~~~~~~~~~~~
  include/boost/uuid/detail/sha1.hpp:179:43: note: passing argument to parameter 'digest' here
  inline void sha1::get_digest(digest_type& digest)

Does this ring a bell, @dbear496?

Oh wait, I was on the wrong git branch, that did not have this PRs changes applied. Apologies, let me try again, 😅