Move OS::Mac::Xcode.provides_autotools? to compat

Closes #125.

Signed-off-by: Misty De Meo <mistydemeo@github.com>

Library/Homebrew/compat.rb

@@ -13,3 +13,4 @@ require "compat/keg"
 require "compat/pathname"
 require "compat/dependency_collector"
 require "compat/language/haskell"
+require "compat/xcode"

Library/Homebrew/compat/xcode.rb

@@ -0,0 +1,11 @@
+module OS
+  module Mac
+    module Xcode
+      extend self
+
+      def provides_autotools?
+        version < "4.3"
+      end
+    end
+  end
+end

Library/Homebrew/os/mac/xcode.rb

@@ -138,10 +138,6 @@ module OS
         end
       end
 
-      def provides_autotools?
-        version < "4.3"
-      end
-
       def provides_gcc?
         version < "4.3"
       end