Add ENV.refurbish_args helper

Rationale: our arg refurbishment is normally only turned on when
called via the `make` wrapper, for compatibility reasons. However,
there are numberous places we'd like this to be turned on elsewhere,
like software that builds via `python setup.py` where bad flags from
the system python can be pulled in.

This helper appends 'O' to CCCFG, which enables refurbishment for
all calls of the compiler shims.

Library/Homebrew/extend/ENV/std.rb

@@ -359,4 +359,7 @@ module Stdenv
       Hardware::CPU.cores
     end
   end
+
+  # This method does nothing in stdenv since there's no arg refurbishment
+  def refurbish_args; end
 end

Library/Homebrew/extend/ENV/super.rb

@@ -295,6 +295,10 @@ module Superenv
     end
   end
 
+  def refurbish_args
+    append 'HOMEBREW_CCCFG', "O", ''
+  end
+
   # m32 on superenv does not add any CC flags. It prevents "-m32" from being erased.
   def m32
     append 'HOMEBREW_CCCFG', "3", ''