Only check the opensslv.h header to find the system openssl version
Only check the opensslv.h header to find the system openssl version

* `openssl version` can be another version than the header, for instance with
  `apt-get install --no-install-recommends ca-certificates libssl1.0-dev` on Ubuntu 18.04:
  https://github.com/rbenv/ruby-build/discussions/2014#discussioncomment-3224237

rbenv/ruby-build,rbenv/ruby-build