audit: don't allow openssl & libressl dependency.

Formulae should not depend on both OpenSSL and LibreSSL (even
optionally). This is to avoid descending into madness where every
formulae that could use LibreSSL has to have option and switching logic.

Homebrew has standardised on OpenSSL and will do so everywhere that
LibreSSL is not a hard requirement.

Library/Homebrew/dev-cmd/audit.rb

@@ -788,6 +788,10 @@ class FormulaAuditor
       problem "Please set plist_options when using a formula-defined plist."
     end
 
+    if text =~ /depends_on\s+['"]openssl['"]/ && text =~ /depends_on\s+['"]libressl['"]/
+      problem "Formulae should not depend on both OpenSSL and LibreSSL (even optionally)."
+    end
+
     return unless text.include?('require "language/go"') && !text.include?("go_resource")
     problem "require \"language/go\" is unnecessary unless using `go_resource`s"
   end