switch to using extend pattern

Library/Homebrew/dependency_collector.rb

@@ -5,6 +5,12 @@ require "requirement"
 require "requirements"
 require "set"
 
+if OS.mac?
+  require "extend/os/mac/ant_dep"
+elsif OS.linux?
+  require "extend/os/linux/ant_dep"
+end
+
 ## A dependency is a formula that another formula needs to install.
 ## A requirement is something other than a formula that another formula
 ## needs to be present. This includes external language modules,
@@ -135,12 +141,6 @@ class DependencyCollector
     end
   end
 
-  def ant_dep(spec, tags)
-    if MacOS.version >= :mavericks || !OS.mac?
-      Dependency.new(spec.to_s, tags)
-    end
-  end
-
   def resource_dep(spec, tags)
     tags << :build
     strategy = spec.download_strategy

Library/Homebrew/extend/os/linux/ant_dep.rb

@@ -0,0 +1,4 @@
+def ant_dep(spec, tags)
+  # Always use brewed ant on Linux
+  Dependency.new(spec.to_s, tags)
+end

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

@@ -0,0 +1,5 @@
+def ant_dep(spec, tags)
+  if MacOS.version >= :mavericks
+    Dependency.new(spec.to_s, tags)
+  end
+end