avidemux: adjust merged patch, use fails_with

Avidemux-2.5.6 had its one patch merged upstream the day this
formula was accepted.  That was hoped for but unexpected.  This
commit adjusts the conditional for def patches so that it only
gets applied to stable.  Fixes a patch failure for 32bit + HEAD.

Also in this commit, remove the hardcoded `ENV.llvm` and switch
to using `fails_with :clang`, surrounded by a conditional so it
can still be built with clang if `--with-debug`.

Closes Homebrew/homebrew#11959.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

Formula/avidemux.rb

@@ -26,12 +26,20 @@ class Avidemux < Formula
   depends_on 'xvid'
   depends_on 'x264'
 
+  # Check if this still exists @ XCode-4.3.4 or 4.4.0.  I think it's fixed then
+  # by llvm in clang svn.  So this will have to persist for older clang.
+  fails_with :clang do
+    build 318
+    cause "error in backend: Couldn't allocate input reg for constraint"
+  end unless ARGV.include? '--with-debug'
+
   def options
     [[ '--with-debug', 'Enable debug build.' ]]
   end
 
   def patches
-    DATA if Hardware.is_32_bit?
+    # Symbols undefined due to optimization.  Fixed in head. Remove @ 2.5.7.
+    DATA if Hardware.is_32_bit? and not ARGV.build_head?
   end
 
   def install
@@ -63,8 +71,6 @@ class Avidemux < Formula
     end
 
 
-    # Force llvm if clang on a normal build, fails_with_clang (being sovled).
-    ENV.llvm if ENV.compiler == :clang and not ARGV.include? '--with-debug'
     # Build the core.
     gettext = Formula.factory('gettext')
     mkdir 'corebuild' do