ctags: Apply patch to fix invalid use of const.

This restores compatibility with llvm.

Closes Homebrew/homebrew#15840.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>

Formula/ctags.rb

@@ -9,14 +9,12 @@ class Ctags < Formula
 
   depends_on :autoconf
 
-  fails_with :llvm do
-    build 2335
-    cause "Resulting executable generates erroneous tag files"
+  def patches
+    # fixes http://sourceforge.net/tracker/?func=detail&aid=3247256&group_id=6556&atid=106556
+    { :p2 => "https://raw.github.com/gist/4010022/8d0697dc87a40e65011e2192439609c17578c5be/ctags.patch" }
   end
 
   def install
-    # See https://trac.macports.org/changeset/93604
-    ENV.O1
     if build.head?
       system "autoheader"
       system "autoconf"