mpack: fix compilation with clang

Fixes Homebrew/homebrew#14375

Formula/mpack.rb

@@ -1,12 +1,20 @@
 require 'formula'
 
 class Mpack < Formula
-  url 'http://ftp.andrew.cmu.edu/pub/mpack/mpack-1.6.tar.gz'
   homepage 'http://ftp.andrew.cmu.edu/pub/mpack/'
-  md5 'a70fa5afa76539a9afb70b9d81568fe8'
+  url 'http://ftp.andrew.cmu.edu/pub/mpack/mpack-1.6.tar.gz'
+  sha1 '7fd3a73e0f131412920b6ff34872e7e7fa03e03b'
+
+  # Fix missing return value; clang refuses to compile otherwise
+  def patches
+    {:p0 => [
+    "https://trac.macports.org/export/96943/trunk/dports/mail/mpack/files/uudecode.c.patch"
+    ]}
+  end
 
   def install
-    system "./configure", "--prefix=#{prefix}", "--mandir=#{man}"
+    system "./configure", "--prefix=#{prefix}",
+                          "--mandir=#{man}"
     system "make install"
   end
 end