superenv/cc: keep exec monkeypatch out of Object

Library/ENV/4.3/cc

@@ -21,18 +21,20 @@ def syspath
     %W{/usr /usr/local}
   end
 end
-def exec *args
-  path = File.expand_path('~/Library/Logs/Homebrew/cc.log')
-  open(path, 'a') do |f|
-    f.print '[', $0
-    f.print " -%s" % ENV['HOMEBREW_CCCFG'] if ENV['HOMEBREW_CCCFG']
-    f.print '] '
-    f.puts args.join(' ')
-    f.puts
-  end
-  Kernel.exec *args
-end if ENV['HOMEBREW_LOG']
 
+module ExecLogExtension
+  def exec *args
+    path = File.expand_path('~/Library/Logs/Homebrew/cc.log')
+    open(path, 'a') do |f|
+      f.print '[', $0
+      f.print " -%s" % ENV['HOMEBREW_CCCFG'] if ENV['HOMEBREW_CCCFG']
+      f.print '] '
+      f.puts args.join(' ')
+      f.puts
+    end
+    Kernel.exec *args
+  end
+end
 
 class Cmd
   def initialize path, args
@@ -206,6 +208,7 @@ if __FILE__ == $PROGRAM_NAME
   end
 
   ####################################################################### main
+  extend(ExecLogExtension) if ENV['HOMEBREW_LOG']
   cmd = Cmd.new($0, ARGV)
   exec "xcrun", cmd.tool, *cmd.args
 end