Separate default rake from rake ci

Rakefile

@@ -11,19 +11,27 @@ begin
 rescue LoadError
 else
   Rake::Task[:rubocop].clear if Rake::Task.task_defined?(:rubocop)
-  if !defined?(::Rubinius)
+  require 'rbconfig'
+  # https://github.com/bundler/bundler/blob/1b3eb2465a/lib/bundler/constants.rb#L2
+  windows_platforms = /(msdos|mswin|djgpp|mingw)/
+  if RbConfig::CONFIG['host_os'] =~ windows_platforms
+    desc 'No-op rubocop on Windows-- unsupported platform'
+    task :rubocop do
+      puts 'Skipping rubocop on Windows'
+    end
+  elsif defined?(::Rubinius)
+    desc 'No-op rubocop to avoid rbx segfault'
+    task :rubocop do
+      puts 'Skipping rubocop on rbx due to segfault'
+      puts 'https://github.com/rubinius/rubinius/issues/3499'
+    end
+  else
     Rake::Task[:rubocop].clear if Rake::Task.task_defined?(:rubocop)
     desc 'Execute rubocop'
     RuboCop::RakeTask.new(:rubocop) do |task|
       task.options = ['--rails', '--display-cop-names', '--display-style-guide']
       task.fail_on_error = true
     end
-  else
-    desc 'No-op rubocop to avoid rbx segfault'
-    task :rubocop do
-      puts 'Skipping rubocop on rbx due to segfault'
-      puts 'https://github.com/rubinius/rubinius/issues/3499'
-    end
   end
 end
 
@@ -37,3 +45,6 @@ Rake::TestTask.new do |t|
 end
 
 task default: [:test, :rubocop]
+
+desc 'CI test task'
+task :ci => [:default]