Automatically link to Homebrew OpenSSL

If a system OpenSSL version was not found or is at version that is incompatible with a Ruby being installed, ruby-build would typically download and compile a new OpenSSL version scoped to that Ruby installation.

Now the `needs_openssl` condition will also check for Homebrew-installed OpenSSL and automatically link to the first one found that satisfies the version requirement. This primarily helps speed up Ruby installation on macOS where the system OpenSSL is never compatible and where Homebrew is a de-facto standard package manager.