chuck: fix build on 10.9

Fixes Homebrew/homebrew#26519.

Formula/chuck.rb

@@ -7,6 +7,15 @@ class Chuck < Formula
 
   def install
     cd "src" do
+      # On 10.9, chuck fails to set flags to link against the
+      # private framework it needs
+      # See: https://github.com/Homebrew/homebrew/issues/26519
+      inreplace 'makefile.osx' do |s|
+        s.change_make_var! 'LINK_EXTRAS',
+          '-F/System/Library/PrivateFrameworks -weak_framework MultitouchSupport'
+        s.remove_make_var! 'ISYSROOT'
+      end
+
       system "make osx"
       bin.install "chuck"
     end