Refactor MacOS check_development_tools usage.

Better use the abstraction layer so e.g. Linux could have similarly
fatal checks for these things.

Library/Homebrew/cmd/install.rb

@@ -223,14 +223,15 @@ module Homebrew
 
   def check_development_tools
     checks = Diagnostic::Checks.new
-    checks.all_development_tools_checks.each do |check|
+    all_development_tools_checks = checks.development_tools_checks +
+                                   checks.fatal_development_tools_checks
+    all_development_tools_checks.each do |check|
       out = checks.send(check)
-      opoo out unless out.nil?
-    end
-    if OS.mac? && MacOS.prerelease?
-      checks.strict_development_tools_checks.each do |strict_check|
-        out = checks.send(strict_check)
-        odie out unless out.nil?
+      next if out.nil?
+      if checks.fatal_development_tools_checks.include?(check)
+        odie out
+      else
+        opoo out
       end
     end
   end

Library/Homebrew/diagnostic.rb

@@ -86,12 +86,17 @@ module Homebrew
       end
       ############# END HELPERS
 
-      def all_development_tools_checks
+      def development_tools_checks
         %w[
           check_for_installed_developer_tools
         ]
       end
 
+      def fatal_development_tools_checks
+        %w[
+        ]
+      end
+
       def check_for_installed_developer_tools
         return if DevelopmentTools.installed?
 

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

 module Homebrew
   module Diagnostic
     class Checks
-      def all_development_tools_checks
+      def development_tools_checks
         %w[
           check_for_unsupported_osx
           check_for_prerelease_xcode
@@ -12,11 +12,16 @@ module Homebrew
         ]
       end
 
-      def strict_development_tools_checks
-        %w[
-          check_xcode_up_to_date
-          check_clt_up_to_date
-        ]
+      def fatal_development_tools_checks
+        if MacOS.prerelease?
+          %w[
+            check_xcode_up_to_date
+            check_clt_up_to_date
+          ]
+        else
+          %w[
+          ]
+        end
       end
 
       def check_for_unsupported_osx