Set -faltivec in CFLAGS on Tiger

Setting -mcpu and -mtune on Tiger with gcc-4.2 exposes a bug in one of the
system headers, causing certain builds to fail. This can be fixed by
adding -faltivec to CFLAGS.

See: http://trac.macports.org/ticket/34213

Library/Homebrew/extend/ENV/std.rb

@@ -324,6 +324,9 @@ module Stdenv
     remove flags, /-msse4(\.\d)?/
     append flags, xarch unless xarch.empty?
     append flags, map.fetch(effective_arch, default)
+
+    # Works around a buggy system header on Tiger
+    append flags, "-faltivec" if MacOS.version == :tiger
   end
 
   # @private