support/scripts/build_release_artifacts: don't build binaries based solely on semver

[ire-and-curses]

PR Structure

• This PR has reasonably narrow scope (if not, break it down into smaller PRs)
• This PR avoids mixing refactoring changes with feature changes (split into two PRs otherwise)
• This PR's title starts with name of package that is most changed in the PR, ex. services/friendbot

Thoroughness

• This PR adds tests for the most critical parts of the new functionality or fixes.
• I've updated any docs (developer docs, .md files, etc...) affected by this change

Release planning

• I've updated the relevant CHANGELOG (here for Horizon) if needed with deprecations, added features, breaking changes, and DB schema changes
• I've decided if this PR requires a new major/minor version according to semver, or if it's only a patch change. The PR is targeted at the next release branch if it's not a patch change.

Summary

Fixes the situation where a tagged semVer release leads to the build system producing junk binary releases, when there is nothing to build. Closes #1208.

Goal and scope

See #1208.

Summary of changes

Build script exits with a log message if there is nothing to build.

Testing

This was tested locally with hardcoded variable names.