autogen 5.18.1

Closes Homebrew/homebrew#23064.

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

Formula/autogen.rb

@@ -2,12 +2,23 @@ require 'formula'
 
 class Autogen < Formula
   homepage 'http://autogen.sourceforge.net'
-  url 'http://ftpmirror.gnu.org/autogen/rel5.17.3/autogen-5.17.3.tar.gz'
-  mirror 'http://ftp.gnu.org/gnu/autogen/rel5.17.3/autogen-5.17.3.tar.gz'
-  sha1 '90c287c6d255c68bb3d7233e31672f0be8c38d07'
+  url 'http://ftpmirror.gnu.org/autogen/rel5.18.1/autogen-5.18.1.tar.gz'
+  mirror 'http://ftp.gnu.org/gnu/autogen/rel5.18.1/autogen-5.18.1.tar.gz'
+  sha1 '53d29cafd187895f795e2ba94b9964f71da93060'
 
   depends_on 'guile'
 
+  fails_with :clang do
+    build 500
+    cause <<-EOS.undent
+      Clang does not appear to be able to handle variables using the name
+      'noreturn' as it is a new keyword in C++11, but it would normally be
+      used as in [[noreturn]] void foo() and not as a variable name. I'm not
+      sure if this is a compiler bug or what, but GCC handles it fine at
+      the moment.
+    EOS
+  end
+
   def install
     system "./configure", "--disable-debug",
                           "--disable-dependency-tracking",