diagnostic: use universal pull request message

Library/Homebrew/diagnostic.rb

@@ -95,6 +95,16 @@ module Homebrew
         ]).freeze
       end
 
+      def please_create_pull_requests(what = "unsupported configuration")
+        <<~EOS
+          You may encounter build failures and other breakages.
+          Please create pull requests instead of asking for help on
+          Homebrew's GitHub, Discourse, Twitter or IRC. You are
+          responsible for resolving any issues you experience, as
+          you are running this #{what}.
+        EOS
+      end
+
       def check_for_installed_developer_tools
         return if DevelopmentTools.installed?
 

Library/Homebrew/extend/os/mac/diagnostic.rb

@@ -60,10 +60,7 @@ module Homebrew
         <<~EOS
           You are using macOS #{MacOS.version}.
           #{who} do not provide support for this #{what}.
-          You will encounter build failures and other breakages.
-          Please create pull requests instead of asking for help on Homebrew's
-          GitHub, Discourse, Twitter or IRC. As you are running this #{what},
-          you are responsible for resolving any issues you experience.
+          #{please_create_pull_requests(what)}
         EOS
       end